The strategic logic was obvious to everyone who looked at a map. Where the Allegheny flows south and the Monongahela flows north, they merge to form the Ohio River, the great highway into the continental interior. Whoever controlled this fork controlled trade, movement, and power across the frontier. In 1754, the French seized the spot, building Fort Duquesne atop a small British outpost called Fort Prince George. Britain sent General Braddock with 1,500 men to take it back. His force was shattered at the Battle of the Monongahela in 1755, ambushed just miles from the fort. It took three more years, the collapse of French supply lines after Fort Frontenac fell, and the Treaty of Easton stripping away Native alliances before the French commander, de Lignery, found himself undermanned and outflanked. He burned Fort Duquesne and retreated north. The French never returned.

Captain Harry Gordon of the 60th Royal American Regiment designed the replacement: a massive pentagram-shaped fortification with bastions at each star point, built between 1759 and 1761. Named Fort Pitt, it was the largest and most sophisticated British fort on the frontier. The engineering was ambitious, straddling two river terraces of different geological ages, requiring enormous fills of gray clay to raise the lower terrace to grade. Archaeological excavations in 2007 uncovered traces of the original palisade line, hand-hewn white oak posts with broadax cuts still visible, and even an 18-foot spruce trunk used as construction fill in 1759. Lead musket balls and salt-glazed stoneware sherds confirmed the dating. The fort was built to project permanence, and it did.

Permanence attracted enemies. In 1763, the Lenape and Shawnee besieged Fort Pitt as part of Pontiac's War, an uprising against colonial encroachment and broken treaties. The fort proved too strong to take by force. During negotiations, Captain Simeon Ecuyer gave two Delaware emissaries blankets exposed to smallpox, an act whose genocidal intent was explicit. Commander William Trent wrote that he hoped it would have "the desired effect." Colonel Henry Bouquet, marching to relieve the fort, discussed similar biological tactics with Commander-in-Chief Jeffery Amherst. On August 1, 1763, Native forces broke off the siege to intercept Bouquet. At the Battle of Bushy Run, Bouquet fought through and relieved the fort on August 10. The episode remains one of the most documented cases of attempted biological warfare in colonial American history.

Fort Pitt found a second life during the American Revolution as headquarters for the western theater. While British forces held Fort Detroit, the Continental Congress dispatched commissioners to Pittsburgh in 1777, including Colonel Samuel Washington, George Washington's younger brother. Their mission: assess threats, cultivate alliances with the Shawnee and Delaware, and plan an offensive against Detroit. George Rogers Clark organized his Illinois expedition at nearby Redstone in 1778, floating down the Monongahela to Fort Pitt for supplies before heading to the Falls of the Ohio. Clark captured Kaskaskia, Cahokia, and Vincennes, and eventually took the British commander Hamilton prisoner in the winter of 1779. The fort served again during the Northwest Indian War and the War of 1812 before fading into the growing borough of Pittsburgh.

By the 20th century, Fort Pitt existed only as archaeology. Pittsburgh commissioned excavations that revealed the fort's foundations, then reconstructed the Monongahela Bastion to house the Fort Pitt Museum. The reconstructed bastion is visible from Mount Washington, a reminder of the fort's scale. But the real survivor is the Blockhouse, a small brick redoubt erected in 1764, believed to be the oldest building in Pittsburgh. It served as a private residence for years before the Daughters of the American Revolution purchased and preserved it. Standing in Point State Park where the rivers still converge, the Blockhouse is the last physical link to the era when this triangle of land was the most fought-over ground in North America.