The impressive fortress of ancient Lilea dates back to the 4th century B.C. The walls have a trapezoidal wall structure and are maintained at a satisfactory height. At times, they are reinforced with rectangular towers, of which the central is distinct at the peak of the acropolis, which would visually monitor the entire valley from the upper reaches of the Kifissos river. Some parts of the ancient fortress have been altered or additions were made during the Frankish occupation (13th-14th centuries). Traces of habitation in the area date back to the early Helladic period (3rd Millennium B.C.). Following the destruction of the cities of Fokida in 346 B.C. by Philip II, King of Macedonia, Lilea was cohabited with its neighboring city, Erocho (the borders of present day Polydrosso). Its walls were most probably built in the post Philip period, during the restructure of the acropolises of Fokida, although samples of an older fortress have been salvaged at the peak of the acropolis.