At this time in 1863,the people of Pittsburgh were pretty concerned about Lee's invading army and where it was headed and started to construct crude forts to hold back the rebels around Pittsburgh.
"Military organizations should also be perfected as rapidly as possible. On Monday thousands of men sauntered idly through the streets, or helped to swell the crowd around drinking houses, and of these a majority would probably have cheerfully attached themselves to any organization for the immediate defense of the city. We trust that the authorities will provide for this contingency to-day, by summoning the idlers to assemble at proper places of rendezvous in the several districts, to organize themselves immediately into military companies, and begin to drill."
From the sound of it a lot of people rushed to defend their local bar.