Dahanu Fort traces a history spanning 400 years, when the Portuguese took over the west coast and segregated the Thane region into two divisions. The fort was under the British and was converted to a jail after independence. Headed by Chimaji Rao Appa, the Marathas took over the fort in 1739.Made up of cut stones, the fort has walls around 10 ft thick and 38 ft high. The terrace of the fort started to deteriorate after 1818.