OROPUS, a Greek seaport, on the Euripus, in the district Heιpdiκη, opposite Eretria. It was a border city between Boeotia and Attica, and its possession was a continual source of dispute between the two countries; but at last it came into the final possession of Athens, and is always alluded to under the Roman empire as an Attic town. The actual harbour, which was called Delphinium, was at the mouth of the Asopus, about a mile north of the city. The famous oracle of Amphiaraus was situated in the territory of Oropus, 12 stadia from the city. A village-still called Oropo occupies the site of the ancient town.