Dorchester's location made it a strategic military site.
Fear of a possible French invasion prompted the construction of a powder magazine and fort from 1757 to 1760.
Originally designed to be constructed using brick, the fort and powder magazine were eventually made of tabby, a concrete material made of lime, sand and oyster shells.
While local materials were used in the construction of the fort, in design it was a simplified version of classic European fortification.
The walls formed a rectangle around the magazine, with sections called half-bastions projecting from each corner.
From these strong points, soldiers could direct deadly fire down the length of adjoining walls.
The French invasion never came, though, and the town apparently saw little activity until the American Revolution in 1775.

In preparation of the impending war, the little town of Dorchester was transformed into a military depot and American troops assembled in town.
 In 1775 the magazine was fortified and the fort was commanded by Capt.
Francis Marion.
After Charleston fell to the British in May 1780, Dorchester became an outpost for British and Loyalist troops.
In December 1781, American forces, led by Colonel Wade Hampton and General Nathanael Greene, advanced on the town and the British were driven out of Dorchester.


After the war, the fort housed a tile yard, with the magazine converted into a kiln for firing clay roofing tiles.
But like the rest of town, the fort was soon abandoned.
Its history was forgotten.
Some people assumed it had been built by the Spanish, and many asserted that it had been built to provide protection from Indians.
Locals eventually gave it the name "Fort Dorchester," even though it never had an official name while it was in use.
Dorchester's location made it a strategic military site. Fear of a possible French invasion prompted the construction of a powder magazine and fort from 1757 to 1760. Originally designed to be constructed using brick, the fort and powder magazine were eventually made of tabby, a concrete material made of lime, sand and oyster shells. While local materials were used in the construction of the fort, in design it was a simplified version of classic European fortification. The walls formed a rectangle around the magazine, with sections called half-bastions projecting from each corner. From these strong points, soldiers could direct deadly fire down the length of adjoining walls. The French invasion never came, though, and the town apparently saw little activity until the American Revolution in 1775.
In preparation of the impending war, the little town of Dorchester was transformed into a military depot and American troops assembled in town.  In 1775 the magazine was fortified and the fort was commanded by Capt. Francis Marion. After Charleston fell to the British in May 1780, Dorchester became an outpost for British and Loyalist troops. In December 1781, American forces, led by Colonel Wade Hampton and General Nathanael Greene, advanced on the town and the British were driven out of Dorchester.

After the war, the fort housed a tile yard, with the magazine converted into a kiln for firing clay roofing tiles. But like the rest of town, the fort was soon abandoned. Its history was forgotten. Some people assumed it had been built by the Spanish, and many asserted that it had been built to provide protection from Indians. Locals eventually gave it the name "Fort Dorchester," even though it never had an official name while it was in use.
Colonial Dorchester State Historic Site