Circa

Circa, ae, v. Circe.

circa
circā adv. I and praep., later for circum. I I. Adv, around, round about, all aro...

An Elementary Latin Dictionary
circa
circā, a later access. form for circum; not freq. before the Aug. per., esp. in Livy and Quintilian ...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.