The river Mazarus, which at that time appears to have formed the boundary with Segesta, was only about 25 km west of Selinunte; and it is certain that at a somewhat later period the territory of Selinunte extended to its banks, and that that city had a fort and emporium at its mouth. On the other side Selinunte's territory certainly extended as far as the Halycus (modern Platani), at the mouth of which it founded the colony of Minoa, or Heracleia, as it was afterward called. It is clear, therefore, that Selinunte had already achieved great power and prosperity; but very little information survives about its history. Like most of the Sicilian cities, it passed from an oligarchy to a tyranny, and about 510 BCE was subject to a despot named Peithagoras, who was overthrown with the assistance of the Spartan Euryleon, one of the companions of Dorieus. Euryleon himself ruled the city, for a little while, but was speedily overthrown and put to death by the Selinuntines. The Selinuntines supported the Carthaginians during the great expedition of Hamilcar (480 BCE); they even promised to send a contingent to the Carthaginian army, but this did not arrive until after Hamilcar's defeat at the Battle of Himera.