Mahim Fort, 16th century fortress in Mahim district, India.

Mahim Fort is a stone fort on Mahim Bay in Mumbai, built from rectangular cut stones in brown, tan and dark grey. Its broad left face shows dark vertical streaks near the corner, a base stained black by tides, and an irregular top edge with small green plants and thin metal rods. A second wall of rough dark stone extends to the right.

In 1516 the Portuguese commander Dom Joao de Monoy entered the Mahim Creek and defeated the fort's commander; the island of Mahim was taken from Bahadur Shah of Gujarat in 1534. In 1661 the Portuguese ceded Mahim as dowry to Charles II of England, and Sir Thomas Grantham strengthened the fort in 1684 as a watchtower against the Portuguese and later the Marathas. A Portuguese attack in 1772 was repelled with cannonballs, damaging Mount Mary's Basilica; the fort then held 100 soldiers and 30 cannons.

The fort's name is tied to Mahim, the neighbourhood it guards, and it is still reached from the Mahim Causeway that links the suburbs to the city. Its Grade I heritage status has not stopped slums from pressing against the walls, and responsibility for the site is shuffled between the state government and the Brihanmumbai Municipal Corporation.

The fort stands off the Mahim Causeway, the road linking the suburbs to the city, so it is reached on foot from the Mahim side. Slums crowd the structure and parts have caved in through tidal erosion, while boulders and crevices up to three metres high lie on the sand. Keep to the outer ground and watch the footing.

In 1772 the fort's garrison of 100 soldiers and 30 cannons drove off a Portuguese attack, and the cannonballs damaged Mount Mary's Basilica nearby. The site is a Grade I heritage structure, yet responsibility for it is split between the state government and the Brihanmumbai Municipal Corporation, and in 2004 five lakh rupees had to be returned because encroachments were not removed.