Siege of Fort Pitt The Siege of Fort Pitt took place in 1763 in what is now the city of Pittsburgh , Pennsylvania , United States . The siege was a part of Pontiac ' s Rebellion , an effort by American Indians to drive the British out of the Ohio Country and back across the Appalachian Mountains . The Indian effort to capture Fort Pitt ultimately failed . Background . Fort Pitt was built in 1758 during the French and Indian War , on the site of what was previously Fort Duquesne . The French abandoned and destroyed Fort Duquesne in November 1758 with the approach of General John Forbes ' s expedition . The Forbes expedition was successful in part because of the Treaty of Easton , in which area American Indians agreed to end their alliance with the French . American Indians — primarily Delawares and Shawnees — made this agreement with the understanding that the British military would leave the area after the war . The Indians wanted a trading post , but they did not want a British fort , or a British garrison , near their villages . The British , however , built Fort Pitt larger and stronger than Fort Duquesne had been . The Siege . In May 1763 , Pontiac ' s Rebellion began at Fort Detroit . After Indians around Pittsburgh heard the news , they attacked Fort Pitt on June 22 , 1763 . Too strong to be taken by force , the fort was kept under siege throughout July . 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 . For General Jeffrey Amherst , who before the war had dismissed the possibility that the Indians would offer any effective resistance to British rule , the military situation over the summer became increasingly grim . He wrote his subordinates and instructed them not to take any Indian prisoners . 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 . Blankets with smallpox . On June 29 , 1763 , a week after the siege began , Bouquet was preparing to lead an expedition to relieve Fort Pitt when he received a letter from Amherst making the following proposal : " Could it not be contrived to send the smallpox among the disaffected tribes of Indians ? We must on this occasion use every stratagem in our power to reduce them . " Bouquet agreed , writing back to Amherst on July 13 , 1763 : " I will try to inoculate the bastards with some blankets that may fall into their hands , and take care not to get the disease myself . " Amherst responded favorably on July 16 , 1763 : " You will do well to inoculate the Indians by means of blankets , as well as every other method that can serve to extirpate this execrable race . " As it turned out , however , officers at the besieged Fort Pitt had already exposed the Indians in just the manner Amherst and Bouquet were discussing . During a parley at Fort Pitt on June 24 , 1763 , Captain Simeon Ecuyer gave representatives of the besieging Delawares two blankets and a handkerchief from the smallpox ward " out of regard to them " after the Delawares pledged to renew their friendship . While the exact meaning of his phrase was unclear , a later invoice appears to clearly establish the purpose was transmittal of smallpox .