Ancient Time-keeping

<p>Many ancient civilizations observed <a href="https://en.wikipedia.org/wiki/Astronomical_object" title="Astronomical object">astronomical bodies</a>, often the <a href="https://en.wikipedia.org/wiki/Sun" title="Sun">Sun</a> and <a href="https://en.wikipedia.org/wiki/Moon" title="Moon">Moon</a>, to determine times, dates, and seasons.<sup id="cite_ref-Chobotovp1_5-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Chobotovp1-5">[5]</a></sup><sup id="cite_ref-bruton_6-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-bruton-6">[6]</a></sup> Methods of <a href="https://en.wikipedia.org/wiki/Sexagesimal" title="Sexagesimal">sexagesimal</a> timekeeping, now common in both <a href="https://en.wikipedia.org/wiki/Western_world" title="Western world">Western</a> and <a href="https://en.wikipedia.org/wiki/Eastern_world" title="Eastern world">Eastern</a> societies, originated nearly 4,000 years ago in <a href="https://en.wikipedia.org/wiki/Mesopotamia" title="Mesopotamia">Mesopotamia</a> and <a href="https://en.wikipedia.org/wiki/Egypt" title="Egypt">Egypt</a>;<sup id="cite_ref-Chobotovp1_5-1" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Chobotovp1-5">[5]</a></sup><sup id="cite_ref-7" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-7">[7]</a></sup> a similar system was developed later in <a href="https://en.wikipedia.org/wiki/Mesoamerica" title="Mesoamerica">Mesoamerica</a>.<sup id="cite_ref-8" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-8">[8]</a></sup> </p>

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The first <a href="https://en.wikipedia.org/wiki/Calendar" title="Calendar">calendars</a> may have been created during the <a href="https://en.wikipedia.org/wiki/Last_glacial_period" title="Last glacial period">last glacial period</a>, by <a href="https://en.wikipedia.org/wiki/Hunter-gatherer" title="Hunter-gatherer">hunter-gatherers</a> who employed tools such as sticks and bones to track the <a href="https://en.wikipedia.org/wiki/Phases_of_the_moon" class="mw-redirect" title="Phases of the moon">phases of the moon</a> or the seasons.<sup id="cite_ref-bruton_6-1" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-bruton-6">[6]</a></sup> </p>

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<a href="https://en.wikipedia.org/wiki/Stone_circle" title="Stone circle">Stone circles</a>, such as England's <a href="https://en.wikipedia.org/wiki/Stonehenge" title="Stonehenge">Stonehenge</a>, were built in various parts of the world, especially in <a href="https://en.wikipedia.org/wiki/Prehistoric_Europe" title="Prehistoric Europe">Prehistoric Europe</a>, and are thought to have been used to time and predict seasonal and annual events such as <a href="https://en.wikipedia.org/wiki/Equinox" title="Equinox">equinoxes</a> or <a href="https://en.wikipedia.org/wiki/Solstice" title="Solstice">solstices</a>.<sup id="cite_ref-bruton_6-2" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-bruton-6">[6]</a></sup><sup id="cite_ref-NISTancient_9-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-NISTancient-9">[9]</a></sup> </p>

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As those <a href="https://en.wikipedia.org/wiki/Megalith" title="Megalith">megalithic</a> civilizations left no <a href="https://en.wikipedia.org/wiki/Recorded_history" title="Recorded history">recorded history</a>, little is known of their calendars or timekeeping methods.<sup id="cite_ref-10" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-10">[10]</a></sup>

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<h3>Ancient Egypt</h3>

<div role="note" class="hatnote">See also: <a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices_in_Egypt" title="History of timekeeping devices in Egypt">History of timekeeping devices in Egypt</a></div>

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<div class="thumbcaption">Ancient Egyptian sundial (c. 1500 BCE) from the Valley of the Kings. Daytime divided into 12 parts.</div>

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<p>The oldest known sundial is from <a href="https://en.wikipedia.org/wiki/Ancient_Egyptian" class="mw-redirect" title="Ancient Egyptian">Egypt</a>; it dates back to around 1500 BCE (19th Dynasty), and was discovered in the Valley of the Kings in 2013.<sup id="cite_ref-One_of_world.27s_oldest_sundials_dug_up_in_Kings.27_Valley.2C_Upper_Egypt_11-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-One_of_world.27s_oldest_sundials_dug_up_in_Kings.27_Valley.2C_Upper_Egypt-11">[11]</a></sup> <a href="https://en.wikipedia.org/wiki/Sundials" class="mw-redirect" title="Sundials">Sundials</a> have their origin in <a href="https://en.wikipedia.org/wiki/Shadow_clock" class="mw-redirect" title="Shadow clock">shadow clocks</a>, which were the first devices used for measuring the parts of a day.<sup id="cite_ref-12" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-12">[12]</a></sup> Ancient Egyptian obelisks, constructed about 3500 BCE, are also among the earliest shadow clocks.<sup id="cite_ref-bruton_6-3" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-bruton-6">[6]</a></sup><sup id="cite_ref-Britannica_13-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Britannica-13">[13]</a></sup><sup id="cite_ref-clockhistory_14-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-clockhistory-14">[14]</a></sup></p>

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<div class="thumbcaption">The <a href="https://en.wikipedia.org/wiki/Luxor_Obelisk" title="Luxor Obelisk">Luxor Obelisk</a> in <a href="https://en.wikipedia.org/wiki/Place_de_la_Concorde" title="Place de la Concorde">Place de la Concorde</a>, <a href="https://en.wikipedia.org/wiki/Paris,_France" class="mw-redirect" title="Paris, France">Paris, France</a></div>

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<p>Egyptian shadow clocks divided <a href="https://en.wikipedia.org/wiki/Daytime_%28astronomy%29" class="mw-redirect" title="Daytime (astronomy)">daytime</a> into 12 parts with each part further divided into more precise parts.<sup id="cite_ref-One_of_world.27s_oldest_sundials_dug_up_in_Kings.27_Valley.2C_Upper_Egypt_11-1" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-One_of_world.27s_oldest_sundials_dug_up_in_Kings.27_Valley.2C_Upper_Egypt-11">[11]</a></sup> One type of shadow clock consisted of a long stem with five variable marks and an elevated crossbar which cast a shadow over those marks. It was positioned eastward in the morning, and was turned west at noon. Obelisks functioned in much the same manner: the shadow cast on the markers around it allowed the Egyptians to calculate the time. The obelisk also indicated whether it was morning or afternoon, as well as the <a href="https://en.wikipedia.org/wiki/Summer_solstice" title="Summer solstice">summer</a> and <a href="https://en.wikipedia.org/wiki/Winter_solstice" title="Winter solstice">winter</a> <a href="https://en.wikipedia.org/wiki/Solstice" title="Solstice">solstices</a>.<sup id="cite_ref-bruton_6-4" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-bruton-6">[6]</a></sup><sup id="cite_ref-NIST_15-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-NIST-15">[15]</a></sup> A third shadow clock, developed c. 1500 BCE, was similar in shape to a bent <a href="https://en.wikipedia.org/wiki/T-square" title="T-square">T-square</a>. It measured the passage of time by the shadow cast by its crossbar on a non-linear rule. The <i>T</i> was oriented eastward in the mornings, and turned around at <a href="https://en.wikipedia.org/wiki/Noon" title="Noon">noon</a>, so that it could cast its shadow in the opposite direction.<sup id="cite_ref-barnett_16-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-barnett-16">[16]</a></sup>

Although accurate, shadow clocks relied on the sun, and so were useless at night and in cloudy weather.<sup id="cite_ref-NIST_15-1" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-NIST-15">[15]</a></sup><sup id="cite_ref-Library_of_Congress_17-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Library_of_Congress-17">[17]</a></sup> The Egyptians therefore developed a number of alternative timekeeping instruments, including water clocks, and a system for tracking star movements. The oldest description of a water clock is from the tomb inscription of the 16th-century BCE Egyptian court official Amenemhet, identifying him as its inventor.<sup id="cite_ref-18" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-18">[18]</a></sup> There were several types of water clocks, some more elaborate than others. One type consisted of a bowl with small holes in its bottom, which was floated on water and allowed to fill at a near-constant rate; markings on the side of the bowl indicated elapsed time, as the surface of the water reached them. The oldest-known waterclock was found in the tomb of <a href="https://en.wikipedia.org/wiki/Pharaoh" title="Pharaoh">pharaoh</a> <a href="https://en.wikipedia.org/wiki/Amenhotep_I" title="Amenhotep I">Amenhotep I</a> (1525–1504 BCE), suggesting that they were first used in ancient Egypt.<sup id="cite_ref-NIST_15-2" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-NIST-15">[15]</a></sup><sup id="cite_ref-19" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-19">[19]</a></sup><sup id="cite_ref-20" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-20">[20]</a></sup> Another Egyptian method of determining the time during the night was using <a href="https://en.wikipedia.org/wiki/Plumb-bob" class="mw-redirect" title="Plumb-bob">plumb-lines</a> called <a href="https://en.wikipedia.org/wiki/Merkhet" title="Merkhet">merkhets</a>. In use since at least 600 BCE, two of these instruments were aligned with <a href="https://en.wikipedia.org/wiki/Polaris" title="Polaris">Polaris</a>, the north <a href="https://en.wikipedia.org/wiki/Pole_star" title="Pole star">pole star</a>, to create a north–south <a href="https://en.wikipedia.org/wiki/Meridian_%28astronomy%29" title="Meridian (astronomy)">meridian</a>. The time was accurately measured by observing certain stars as they crossed the line created with the <i>merkhets</i>.<sup id="cite_ref-NIST_15-3" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-NIST-15">[15]</a></sup><sup id="cite_ref-Time_in_History_21-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Time_in_History-21">[21]</a></sup></p>

<h3>Ancient Greece and Rome</h3>

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<div class="thumbcaption"><a href="https://en.wikipedia.org/wiki/Ctesibius" title="Ctesibius">Ctesibius</a>'s clepsydra from the 3rd century BCE. <i>Clepsydra</i>, literally <i>water thief</i>, is the Greek word for <i>water clock</i>.<sup id="cite_ref-22" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-22">[22]</a></sup></div>

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<p><a href="https://en.wikipedia.org/wiki/Water_clock" title="Water clock">Water clocks</a>, or clepsydrae, were commonly used in <a href="https://en.wikipedia.org/wiki/Ancient_Greece" title="Ancient Greece">Ancient Greece</a> following their introduction by <a href="https://en.wikipedia.org/wiki/Plato" title="Plato">Plato</a>, who also invented a water-based <a href="https://en.wikipedia.org/wiki/Alarm_clock" title="Alarm clock">alarm clock</a>.<sup id="cite_ref-23" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-23">[23]</a></sup><sup id="cite_ref-answers.com_24-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-answers.com-24">[24]</a></sup> One account of Plato's alarm clock describes it as depending on the nightly overflow of a vessel containing lead balls, which floated in a columnar vat. The vat held a steadily increasing amount of water, supplied by a cistern. By morning, the vessel would have floated high enough to tip over, causing the lead balls to cascade onto a copper platter. The resultant clangor would then awaken Plato's students at the <a href="https://en.wikipedia.org/wiki/Platonic_Academy" title="Platonic Academy">Academy</a>.<sup id="cite_ref-25" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-25">[25]</a></sup> Another possibility is that it comprised two jars, connected by a <a href="https://en.wikipedia.org/wiki/Siphon" title="Siphon">siphon</a>. Water emptied until it reached the siphon, which transported the water to the other jar. There, the rising water would force air through a whistle, sounding an alarm.<sup id="cite_ref-answers.com_24-1" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-answers.com-24">[24]</a></sup> The Greeks and <a href="https://en.wikipedia.org/wiki/Chaldean_Dynasty" class="mw-redirect" title="Chaldean Dynasty">Chaldeans</a> regularly maintained timekeeping records as an essential part of their astronomical observations.

<a href="https://en.wikipedia.org/wiki/Ancient_Greece" title="Ancient Greece">Greek</a> astronomer, <a href="https://en.wikipedia.org/wiki/Andronicus_of_Cyrrhus" title="Andronicus of Cyrrhus">Andronicus of Cyrrhus</a>, supervised the construction of the <a href="https://en.wikipedia.org/wiki/Tower_of_the_Winds" title="Tower of the Winds">Tower of the Winds</a> in Athens in the 1st century BCE.

In Greek tradition, clepsydrae were used in <a href="https://en.wikipedia.org/wiki/Court" title="Court">court</a>; later, the <a href="https://en.wikipedia.org/wiki/Ancient_Rome" title="Ancient Rome">Romans</a> adopted this practice, as well. There are several mentions of this in historical records and literature of the era; for example, in <i><a href="https://en.wikipedia.org/wiki/Theaetetus_%28dialogue%29" title="Theaetetus (dialogue)">Theaetetus</a></i>, <a href="https://en.wikipedia.org/wiki/Plato" title="Plato">Plato</a> says that "Those men, on the other hand, always speak in haste, for the flowing water urges them on".<sup id="cite_ref-Water_clocks_in_court_26-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Water_clocks_in_court-26">[26]</a></sup> Another mention occurs in <a href="https://en.wikipedia.org/wiki/Lucius_Apuleius" class="mw-redirect" title="Lucius Apuleius">Lucius Apuleius</a>' <i><a href="https://en.wikipedia.org/wiki/The_Golden_Ass" title="The Golden Ass">The Golden Ass</a></i>: "The Clerk of the Court began bawling again, this time summoning the chief witness for the prosecution to appear. Up stepped an old man, whom I did not know. He was invited to speak for as long as there was water in the clock; this was a hollow globe into which water was poured through a funnel in the neck, and from which it gradually escaped through fine perforations at the base".<sup id="cite_ref-27" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-27">[27]</a></sup> The clock in Apuleius's account was one of several types of water clock used. Another consisted of a bowl with a hole in its centre, which was floated on water. Time was kept by observing how long the bowl took to fill with water.<sup id="cite_ref-Waterclockhistory_28-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-Waterclockhistory-28">[28]</a></sup>

Although clepsydrae were more useful than sundials—they could be used indoors, during the night, and also when the sky was cloudy—they were not as accurate; the Greeks, therefore, sought a way to improve their water clocks.<sup id="cite_ref-29" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-29">[29]</a></sup> Although still not as accurate as sundials, Greek water clocks became more accurate around 325 BCE, and they were adapted to have a face with an hour hand, making the reading of the clock more precise and convenient. One of the more common problems in most types of clepsydrae was caused by <a href="https://en.wikipedia.org/wiki/Water_pressure" class="mw-redirect" title="Water pressure">water pressure</a>: when the container holding the water was full, the increased pressure caused the water to flow more rapidly. This problem was addressed by Greek and Roman <a href="https://en.wikipedia.org/wiki/Horology" title="Horology">horologists</a> beginning in 100 BCE, and improvements continued to be made in the following centuries. To counteract the increased water flow, the clock's water containers—usually bowls or jugs—were given a conical shape; positioned with the wide end up, a greater amount of water had to flow out in order to drop the same distance as when the water was lower in the cone. Along with this improvement, clocks were constructed more elegantly in this period, with hours marked by gongs, doors opening to miniature figurines, bells, or moving mechanisms.<sup id="cite_ref-NIST_15-4" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-NIST-15">[15]</a></sup> There were some remaining problems, however, which were never solved, such as the effect of temperature. Water flows more slowly when cold, or may even freeze.<sup id="cite_ref-30" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-30">[30]</a></sup>

Between 270 BCE and 500 CE, <a href="https://en.wikipedia.org/wiki/Hellenistic_civilization" class="mw-redirect" title="Hellenistic civilization">Hellenistic</a> (<a href="https://en.wikipedia.org/wiki/Ctesibius" title="Ctesibius">Ctesibius</a>, <a href="https://en.wikipedia.org/wiki/Hero_of_Alexandria" title="Hero of Alexandria">Hero of Alexandria</a>, <a href="https://en.wikipedia.org/wiki/Archimedes" title="Archimedes">Archimedes</a>) and <a href="https://en.wikipedia.org/wiki/Ancient_Rome" title="Ancient Rome">Roman</a> <a href="https://en.wikipedia.org/wiki/Horology" title="Horology">horologists</a> and <a href="https://en.wikipedia.org/wiki/Astronomer" title="Astronomer">astronomers</a> began developing more elaborate mechanized water clocks. The added complexity was aimed at regulating the flow and at providing fancier displays of the passage of time. For example, some water clocks rang <a href="https://en.wikipedia.org/wiki/Bell_%28instrument%29" class="mw-redirect" title="Bell (instrument)">bells</a> and <a href="https://en.wikipedia.org/wiki/Gong" title="Gong">gongs</a>, while others opened doors and windows to show figurines of people, or moved pointers, and dials. Some even displayed <a href="https://en.wikipedia.org/wiki/Astrology" title="Astrology">astrological</a> models of the universe.

Although the Greeks and Romans did much to advance water clock technology, they still continued to use shadow clocks. The mathematician and astronomer <a href="https://en.wikipedia.org/wiki/Theodosius_of_Bithynia" title="Theodosius of Bithynia">Theodosius of Bithynia</a>, for example, is said to have invented a universal sundial that was accurate anywhere on Earth, though little is known about it.<sup id="cite_ref-oconnor_31-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-oconnor-31">[31]</a></sup> Others wrote of the sundial in the mathematics and literature of the period. <a href="https://en.wikipedia.org/wiki/Marcus_Vitruvius_Pollio" class="mw-redirect" title="Marcus Vitruvius Pollio">Marcus Vitruvius Pollio</a>, the Roman author of <i><a href="https://en.wikipedia.org/wiki/De_Architectura" class="mw-redirect" title="De Architectura">De Architectura</a></i>, wrote on the mathematics of <a href="https://en.wikipedia.org/wiki/Gnomon" title="Gnomon">gnomons</a>, or sundial blades.<sup id="cite_ref-thayer_32-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-thayer-32">[32]</a></sup> During the reign of <a href="https://en.wikipedia.org/wiki/Augustus" title="Augustus">Emperor Augustus</a>, the Romans constructed the largest sundial ever built, the <a href="https://en.wikipedia.org/wiki/Solarium_Augusti" title="Solarium Augusti">Solarium Augusti</a>. Its gnomon was an obelisk from <a href="https://en.wikipedia.org/wiki/Heliopolis_%28ancient_Egypt%29" class="mw-redirect" title="Heliopolis (ancient Egypt)">Heliopolis</a>.<sup id="cite_ref-33" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-33">[33]</a></sup> Similarly, the obelisk from <a href="https://en.wikipedia.org/wiki/Campus_Martius" title="Campus Martius">Campus Martius</a> was used as the gnomon for Augustus's zodiacal sundial.<sup id="cite_ref-story_of_time_34-0" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-story_of_time-34">[34]</a></sup> <a href="https://en.wikipedia.org/wiki/Pliny_the_Elder" title="Pliny the Elder">Pliny the Elder</a> records that the first sundial in Rome arrived in 264 BCE, looted from <a href="https://en.wikipedia.org/wiki/Catania" title="Catania">Catania</a>, <a href="https://en.wikipedia.org/wiki/Sicily" title="Sicily">Sicily</a>; according to him, it gave the incorrect time until the markings and angle appropriate for Rome's latitude were used—a century later.<sup id="cite_ref-35" class="reference"><a href="https://en.wikipedia.org/wiki/History_of_timekeeping_devices#cite_note-35">[35]</a></sup></p>

Ancient Time-keeping

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