In the valley of the river Kephissus lay two of the most important towns of ancient Phocis, namely Lilaea and Erochos (present-day Polydroso). The broader region was first inhabited in the 3rd millennium B.C., whereas archaeological finds attest to the existence of settlement in the Geometric period as well. 

The town was named after the nymph Lilaea, daughter of the deified river Kephissus, son of Oceanus, by the springs of which it was built. 

Architectural parts close to the springs of St. Eleoussa attest to the existence of a fountain as well as to a temple dedicated to Kephissus, which is located on the nearby terrace, supported by a polygonal wall. At the same location stand the ruins of the Early Byzantine basilica of St. Christopher whereas to the east is preserved the church of St. Eleoussa, dated to the Middle Byzantine Period. On the hill "Pyrgos" or "Palaeokastro" is maintained large part of the sturdy fortification wall of the city, which was rebuilt after its destruction by Philip II of Macedonia in 346 B.C., following the general project of the reconstruction of the Phocian citadels. 

The town Erochos, which has been identified with the remains on the hill of Agios Vassileios (St. Basil) at a distance of 1 klm from the fountain of St. Eleoussa, formed, together with Lilaea, the new foundation after the destruction of the Phocian cities by Philip II. Within its territory there was a rural sanctuary dedicated to Demeter. The excavation carried out by Christos Karouzos in 1928-1934 revealed a square precinct with rooms and a multitude of finds, such as clay figurines, jewellery, pottery vessels etc. These finds attest to a continuous use of the sanctuary from the Late Archaic to the Hellenistic period.