The town of Orhangazi district of Bursa province is located on the southern shore of Lake Iznik, 1.5 km from the lake and 16 km from the district center.
According to ancient Greek sources, Thassos, one of the Argonauts, founded the town, whose old name was Pthapolis in ancient geography. When the Argonauts came to this region during a break, Thassos' close friend Soloeis died by throwing himself into Kocadere as a result of a hopeless love. For this reason, Kocadere was named Soloeis. In Thassos, he founded a city called Pthapolis on the edge of the stream. The name Pthapolis means the home of Apollo. Soloeis' brothers were left in the village. Prof. Dr. Bilge Umar is of the opinion that it came from Soloi, a corruption from Saluwa, meaning “beautiful light”, and that it took this form with the suffix eis, which means “people” in the Hellenic language. The name of the town is thought to have come from here because it is located right on the edge of the soloeis stream.
In 1945, archaeological surveys conducted by Prof. Dr. Şevket Aziz Kansu in Sölöz show that the settlement here dates back to the Chalcolithic Age. As a result of the research, very old settlement remains and a mound were found in the area where the village is located. The mound, located near the stream passing through the village, dates back to the Stone Age. There are dense remains of the mound on the elevation west of Kocadere.
The town, which was known as Muslim Sölöz during the Ottoman period, gained importance in this period. Ali Pasha, who was martyred during the siege of Petervradin in 1717