 He first invaded the island of Kos, a very lucrative conquest (and probably the main reason for the invasion) as the Ptolemies of Egypt and many other nations and people (like the Jews of Alexandria) had stashed part of their treasury there.The people of Kos did not put up a fight and received Mithridates as a liberator not a conqueror.Besides the treasuries Mithridates got a hold of young prince Ptolemy Auletes, who was being held safe on Kos.