post-era; after the epoch
Used in historical or chronological contexts to refer to the period after a specific era or epoch, often in contrast to 紀元前 (pre-era). Can function as a noun or adverbially.
These ruins are from the post-era period.
I am researching post-era history.
紀元前 marks years before the Common Era, while 紀元後 marks years after it, as in 紀元前500年 vs 紀元後500年.
Compound of 紀元 (epoch, era) and 後 (after). The exact historical derivation is uncertain, but the term is conventionally used in chronological contexts.