The siege was a part of Pontiac’s War ( also known as a pan-Indian uprising), an effort by Native Americans to remove the British from the Ohio Country and Allegheny Plateau after they refused to honor their promises and treaties to leave voluntarily following the defeat of the French. This effort, lead by Pontiac, an Ottawa warchief, began In May 1763, at Fort Detroit , and involved the western Lenape, Mingos, and Shawnee. As the conflict swept across the Old Northwest, 600 frightened settlers and a garrison of 125 determined British soldiers, led by Captain Simon Ecuyer, a professional Swiss soldier of the Royal American Regiment, came under siege at Fort Pitt. After Indians around Pittsburgh heard the news, they attacked Fort Pitt on June 22, 1763. The small settlement had acquired that name on 27 November, 1758 from General Forbes. Too strong to be taken by force, the fort was kept under siege throughout July. Captain Ecuyer was facing a threat inside the fort as well. Possibly due to these cramped and overcrowded conditions people began to fall ill with smallpox.
Meanwhile, Delaware and Shawnee war parties raided deep into the Pennsylvania settlements, taking captives and killing unknown numbers of men, women, and children. Panicked settlers fled eastwards, all the way to Philadelphia. The siege didn’t let up until August 1, 1763, when most of the Indians broke off from Fort Pitt in order to intercept a body of 500 British troops marching to the fort under Colonel Henry Bouquet. On August 5, these two forces met at the Battle of Bushy Run. Bouquet fought off the attack and relieved Fort Pitt on August 20.