Starosel (Bulgarian: Старосел) is a village in central Bulgaria, Hisarya Municipality, Plovdiv Province. It lies at the foot of the Sredna Gora mountain range along the shores of Pyasachnik River.
Starosel is known for the abundance of ancient Neolithic and Thracian sites, with some finds dating as far back as the 5th-6th millennium BC. Evidence from 20th-century excavations reveals that the village burgeoned into an important and wealthy Thracian city in the 5th century BC.
Among its main features are the underground temple, the largest of its kind in the Balkan Peninsula, built under the Chetinyova Mogila (tumulus) and a mausoleum. The temple, as well as the nearby Thracian king's residence under Mount Kozi Gramadi, likely date to the reign of Amatokos II (359-351 BC).
Another important site, the Horizont tumulus, contains the only known Thracian temple to feature a colonnade (a Doric one). It is one of ten tumuli located within the location range.