Ischia is an Italian island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about 30 km (19 mi) from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately 10 km (6 mi) east to west and 7 km (4 mi) north to south and has about 34 km (21 mi) of coastline and a surface area of 46.3 km² (17.9 sq mi). It is volcanic and almost entirely mountainous; the highest peak is Mount Epomeo, at 788 m (2,585 ft). The island is very densely populated, with 62,000 residents.