M. Castricius, a Roman knight of business standing whose dealings recur in Cicero's correspondence with Atticus (slave purchases at Ad Att. 12.30; account dispute at 2.7); a different Castricius is named at Verr. 2.3.185 as the recipient of a gold ring presented in public by Verres. The financial Castricius of the Atticus letters is in view here.