A limestone ridge rising to 678m/2,225ft separates the north of the island from the south, in which most of the population has been concentrated since ancient times. From the foot of the hills, a fertile plain extends south to the island's chief town and port, Kálymnos (formerly called Póthia; pop. 9,500; radioactive springs). Its handsome houses
, in the neo-classical style popular in the 19th century, rise above the harbor on the gentle slopes fringing the bay. There is a small museum containing Neolithic material and finds from the sanctuary of Delian Apollo.