An island of 235 acres (103 hectares) at the northern end of the East River, it is legally part of Manhattan. Purchased from a local Native American tribe in 1637 by the Dutch governor general Wouter van Twiller, it was sold as farmland after the American Revolution to the brothers Jasper and Bartholomew Ward. After the island was acquired by the city in 1855 it was used successively for a potter's field, a hospital for destitute immigrants, an auxiliary immigration station, and the City Asylum (an early mental institution). The asylum later became the Manhattan State Hospital and then the Manhattan Psychiatric Center; one of its buildings is now occupied by a men's shelter. The island became the site in 1937 of one of the largest sewage disposal plants in the world, and later of the training school for the city's fire department. Much of the island is now a park, accessible from Manhattan by a footbridge over the Harlem River. Ward's Island is connected by a landfill to Randall's Island and is traversed by the Triborough Bridge and the Hell Gate Bridge.