Khanderi is a fortified island 20 km off the coast of Mumbai

Mumbai

Mumbai , formerly known as Bombay in English, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million...

. This along with its sister fort Underi

Underi

Underi is a fortified island near the mouth of Mumbai harbour south of Prong's Lighthouse. It is a companion fort to Khanderi and currently lies in Raigad district, Maharashtra. These islands of Khanderi and Underi served as one of the landmarks for ships entering Mumbai harbour...

 formed the major fortification along the Mumbai coast. This was built by Shivaji in 1660 CE
to keep a check on the Siddi

Siddi

The Siddi, Siddhi, or Sheedi , also known as Habshi, are an Indian and Pakistani ethnic group of Afro-Arab and/or Black African descent. The Siddi population is currently estimated to be 20,000–55,000, with Gujarat and Hyderabad in India the main population centre. Siddis are mainly Sufi Muslims,...

s at Murud-Janjira

Murud-Janjira

Murud-Janjira is the local name for a fort situated on an island just off the coastal village of Murud, in the Raigad district of Maharashtra, India...

fort. However later on it lost its importance. Most of the fort is still intact the most prominent structure is a lighthouse built in 1837. It can only be accessed with the permission of the Bombay Port Trust.