Why did Captain Alexander Grant establish a British base at Banjul Island in 1816?

In 1816, Captain Alexander Grant established a British base on Banjul Island (which he renamed St. Mary’s) for two primary reasons:

• Suppressing the Slave Trade: The British Colonial Office ordered the establishment of a military post to provide a base from which the British navy could effectively control and suppress the slave trade in the region.12
• Commercial Interests: The base was intended to serve as a trade outlet for merchants who had been ejected from Senegal after that territory was restored to France.2

To secure this position, Grant purchased the island from the king of Kombo, constructed barracks, and set up an artillery battery to control access to the Gambia River. The resulting settlement, originally named Bathurst, eventually became the capital of The Gambia and is known today as Banjul.12