American Civil War: The Allegheny Arsenal explosion in Lawrenceville, Pennsylvania results in the single largest civilian disaster during the war.

The Allegheny Arsenal, established in 1814, was an important supply and manufacturing center for the Union Army during the American Civil War, and the site of the single largest civilian disaster during the war. It was located in the community of Lawrenceville, Pennsylvania, which was annexed by the city of Pittsburgh in 1868.

Lawrenceville is one of the largest neighborhood areas in Pittsburgh in the U.S. state of Pennsylvania. It is located northeast of downtown, and like many of the city's riverfront neighborhoods, it has an industrial past. The city officially divides Lawrenceville into three neighborhoods, Upper Lawrenceville, Central Lawrenceville, and Lower Lawrenceville, but these distinctions have little practical effect. Accordingly, Lawrenceville is almost universally treated as a single large neighborhood.

September 17 is the 260th day of the year in the Gregorian calendar; 105 days remain until the end of the year.