Sindhudurg Sindhudurg Fort ( Marathi सिंधुदुर्ग किल्ला ) is a fort that occupies an islet in the Arabian Sea , just off the coast of Maharashtra in Western India . The fortress lies on the shore of Malvan town of Sindhudurg District in the Konkan region of Maharashtra, 450 kilometers (280 mi) south of Mumbai . It is a protected monument. History:- This fort was constructed by Shri Chhatrapati Shivaji Maharaj , the Chhatrapati of the Maratha Empire . The construction was done under the supervision of Hiroji Indulkar, in the year 1656. Structural Details:- Over 4000 mounds of iron were used in the casting and foundation stones were firmly laid down. Construction started on 25 November 1664. Built over a period of three years (1664–67), the sea fort is spread over 48 acres (190,000 m 2 ) with a two-mile (3 km) long rampart, and walls that are 30 feet (9.1 m) high and 12 feet (3.7 m) thick. The massive walls were designed to serve as a deterr