A Relic

1. That which remains; that which is left after loss or decay; a remaining portion.
2. Something old and outdated, possibly kept for sentimental reasons.
3. (religion) A part of the body of a saint, or an ancient religious object, kept for veneration.

By comparison with synonyms, relic emphasizes age, and to some degree value – a “relic of a lost civilization”.

(that which remains): remnant, remainder, residue, lave

(that which is regarded as ancient, rare, or sacred): halidom