Cius was strategically placed at the head of a gulf in the Propontis, called the gulf of Cius, or Cianus Sinus. Herodotus calls it Cius of Mysia; and also Xenophon, from which it appears that Mysia, even in Xenophon's time, extended at least as far east as the head of the gulf of Cius. Pliny the Elder reports that Cius was a Milesian colony. It was at the foot of Mount Arganthonius, and there was a myth that Hylas, one of the companions of Heracles on the voyage to Colchis, was carried off by the nymphs when he went to get water here; and also that Cius, another companion of Heracles, on his return from Colchis, stayed here and founded the city, to which he gave his name. Pliny mentions a river Hylas and a river Cius here, one of which reminds us of the name of the youth who was stolen by the nymphs, and the other of the mythical founder. The Cius may be the channel by which the lake Ascania discharges its waters into the gulf of Cius; though Pliny speaks of the Ascanium flumen as flowing into the gulf, and we must assume that he gives this name to the channel which connects the lake and the sea. If the river Cius is not identical with this channel, it must be a small stream near Cius. As Ptolemy speaks of the outlets of the Ascanius, it has been conjectured that there may have been two, and that they may be the Hylas and Cius of Pliny; but the plural ἐκβολαί does not necessarily mean more than a single mouth; and Pliny certainly says that the Ascanius flows into the gulf. However, his geography is a constant cause of difficulty. The position of Cius made it the port for the inland parts, and it became a place of much commercial importance. Pomponius Mela calls it the most convenient emporium of Phrygia, which was at no great distance from it.