The fort was constructed in 1863-64 during the Civil War as an earthwork battery on the south shore of the mouth of the Columbia River, and was known as the Fort at Point Adams. It was later Fort Stevens in 1865, in honor of the former territorial governor of Washington, Isaac Stevens, who had been killed in action. Fort Stevens was the primary military installation in what became the "Three Fort Harbor Defense System" at the mouth of the Columbia River. The other forts were the Post at Cape Disappointment, later Fort Cape Disappointment and later Fort Canby, built at the same time as Fort Stevens, and Fort Columbia, built between 1896 and 1904. Both are on the Washington side of the river. The fort was meant to defend the mouth of the Columbia from potential British attack during the Pig War of 1859 and subsequent ongoing regional tensions through 1870 in the San Juan Islands, and was important during the 1896-1903 Alaska Boundary Dispute, when British-American tensions again were high and the two countries were on the brink of war.