When Massachusetts troops marched through the city on April 19, 1861, en route to Washington, D.C., a rebel mob attacked; 4 soldiers and 12 rioters were dead, and 36 soldiers and uncounted rioters had been injured. Governor Thomas Hicks realized action needed to be taken. He convened a special session of the General Assembly but moved its location to a site in Frederick, a distance from the secessionist groups. In doing this and by other actions, Hicks managed to neutralize the General Assembly to avoid Maryland's secession from the Union, becoming a hero in the eyes of the Unionists in the state. Meanwhile, pro-Confederate gangs burned the bridges connecting Baltimore and Washington to the North, and cut the telegraph lines. Lincoln sent in federal troops under Gen. Ben Butler; they seized the city, imposed martial law, and arrested leading Confederate spokesmen. The prisoners were later released and the rail lines reopened, making Baltimore a major Union base during the war.