Bygone (adjective)

1. Belonging to the past; no longer current or happening.
2. No longer in existence.

Origin:

Late 16th century (as a noun in the sense 'past events'): from by + gone.

Examples:

1. The bygone era of chivalry and knights in shining armor.
2. The bygone days of steam trains and horse-drawn carriages.
3. The town was a shadow of its former self, a reminder of bygone prosperity.
4. He spent hours poring over maps of the bygone empire.
5. The bygone civilization left behind only ruins and mystery.