Panaji, the capital of Goa, is situated next to the mouth of the river Mandovi. At the narrowest point of the estuary, on the northern bank, lies a centuries-old historical defense structure called Reis Magos Fort. The Portuguese built the fort in 1551. Due to its strategic location and skillful construction, the fort was nearly impregnable.

This fort predates the much larger Fort Aguada by half a century. This site originally housed a military outpost Adil Shahi Sultanate of Bijapur built in 1493. When the Portuguese defeated the Sultanate, they constructed the first fort here in 1551 as a line of defense for the then capital of Old Goa (which was also called Velha Goa or Ela). The fort was subsequently enlarged on various occasions and then completely rebuilt in 1707.

The two-story fort had an arsenal of 33 cannons to defend the estuary. It also contained a freshwater spring that supplied troops with water, and impressive flights of stone stairs. The fort is located at the narrowest point of the river Mandovi making it a great spot to monitor and control the movement of boats and ships in the estuary. The possibility of enemy ships sneaking in was almost impossible.

The fort was also used to accommodate Viceroys and other dignitaries newly arrived from, or en route to, Lisbon.

The British army captured and controlled the fort from 1798 to 1813. Later, it was abandoned and used as a prison until 1993.

The fort has recently been expertly restored. An exhibit on the upper level of the fort displays interesting photos and information about the history of the fort and the area. The gun loops at the base of the fort today house the artwork of legendary Indian cartoonist and painter Mario Miranda.

Reis Magos Fort boasts impressive walls, turrets, gun holes, stone stairs, corridors, old cannons, dungeon-like rooms, and fantastic views of the Arabian Sea, the mouth of the river Mandovi, and the capital city of Panaji. The fort is one of the oldest in Goa.