The first mention of Kolaba fort is when it was chosen by Shivaji to be fortified after the whole of South Konkan came under his command. In 1662, he strengthened and fortified Kolaba fort to make it one of his chief naval stations. The command of the fort was given to Darya Sagar and Manik Bhandari under whom Kolaba fort became the centre of Maratha attacks on British ships. [2]

In 1713 under a treaty with Peshwa Balaji Vishwanath, Kolaba along with several other forts was given over to Kanhoji Angre. He used it as his main base from which to launch raids on British ships. In 1722, the Bombay Government incensed at Angre's activities, joined the Portuguese in an

 

expedition against Kolaba. A Portuguese land force and three English ships of the line under Commodore Mathews co-operated but the attempt failed owing to the "cowardice of the Portuguese". About this time Kolaba is described by Hamilton as a fort built on a rock, a little way from the mainland and at high water an island.

 
     
 

The average height of the fort walls is 25 feet. It has two main entrances, one on the sea side and the other towards Alibag. An interesting feature of this fort is that it has freshwater wells in its premises even though it is a seaside fort. In the monsoons, the fort can be reached by wading through waist-deep water at low tide. However, at high tide, boats must be used to reach it.

The Siddhivinayak temple inside the fort was built by Raghoji Angre in 1759.