Assa (Ancient Greek: Ἄσσα), also known as Assera (Ἄσσηρα), was a town of Chalcidice, in ancient Macedonia, on the Singitic Gulf. It is cited by Herodotus as one of the cities—together with Pilorus, Singus and Sarte—located near Mount Athos which Xerxes ordered to open a channel through which his fleet passed, and from which he recruited troops in his expedition of the year 480 BCE against Greece. It belonged to the Delian League since it appears in the tribute registry of Athens from 454/3 to 433/2 BCE. Its site is tentatively located near modern .