Crossing the Potomac river, Dam #3 (known as the Government Dam), was built in 1799 to provide water power to the national armory at Harpers Ferry. The dam was initially a wooden structure filled with loose rocks secured at various points to large rock formations in the river. The dam was rebuilt numerous times, most notably in 1809 and in 1820. In the mid nineteenth century, it was thought that the New Armory Dam would replace Dam #3. However, for the reasons mentioned in the supplement to post #15, the former structure was never completed. In 1833 the Chesapeake & Ohio Canal Company added a guard lock directly upstream from Dam #3 in order to regulate water levels within the canal.