During the course of the Fourth War of the Diadochi Ptolemy I Soter captures Kos from Antigonus I Monophthalmus, incorporating it into his kingdom. In the Hellenistic period, Kos attained the zenith of its prosperity. Kos was valued by the Ptolemies, who used it as a naval outpost to oversee the Aegean. As a seat of learning, it arose as a provincial branch of the museum of Alexandria, and became a favorite resort for the education of the princes of the Ptolemaic dynasty. During the Hellenistic age, there was a medical school; however, the theory that this school was founded by Hippocrates (see below) during the Classical age is an unwarranted extrapolation. It was the home of the major Hellenistic poet-scholar Philitas.