Oropos is a small town and a municipality in East Attica, Greece.

The Amphiareion of Oropos, situated in the hills 6 km southeast of the fortified port of Oropos, was a sanctuary dedicated in the late 5th century BCE to the hero Amphiaraos, where pilgrims went to seek oracular responses and healing. It became particularly successful during the 4th century BCE, to judge from the intensive building at the site. The hero Amphiaraos was a descendant of the seer Melampos and initially refused to participate in the attack on Thebes because he could foresee that it would be a disaster. In some versions of the myth, the earth opens and swallows the chariot of Amphiaraos, transforming him into a chthonic hero. Today the site is found east of the modern town Markopoulo Oropou in the Oropos municipality of Attica, Greece.