After the fall of Fort Sumter, South Carolina to the Confederates, it was decided that the Nation's Capital was in need of defenses. Among the first fortifications were built were the ones at the three crossings of the Potomac River - Chain Bridge (Fort Ethan Allen), Aqueduct Bridge (Fort Corcoran) and Long Bridge (Fort Jackson). Over time the Arlington Line of fortifications developed beginning at the Potomac and encircling the western side of the Capital on the Virginia side. The line consisted of about 30 forts, augmented by interwoven artillery batteries. Among this extensive line of fortifications was Fort Cass (originally called Fort Ramsay) that was built in August 1861 within the 1,100 acres of the Custis-Lee estate. It was a lunette which had emplacements for 13 artillery pieces - guns. Constructed by the 9th Massachusetts Infantry Regiment, the name of the fortification was later changed to honor Colonel Thomas Cass, the regiment's first commander who was killed in 1862.