This link will help....
http://lcweb2.loc.gov/cocoon/legacies/PA/200002950.html

and I quote from that page

"The first Scottish tartan kilt was first seen in the Laurel Highlands of western Pennsylvania in the year 1758 when soldiers of the famous 42nd Highland Regiment (Black Watch), under the command of General John Forbes, marched westward from Philadelphia to wrest control of the fort at the forks of the Ohio from the French. At Ligonier, which lay some 20 leagues west of Fort Duquesne, Forbes had a wooden fort constructed that would serve as a staging area for the final assault. The fort was named after Lord Ligonier, who was the Commander in Chief of the British Army at that time. The town of Ligonier, scene of the Ligonier Highland Games, takes its name from that fort. General Forbes led his troops to a victory that saw the French fleeing the area never to return. Fort Duquesne was burned to the ground, and over its ashes rose a settlement named "Pittsburgh" by Forbes in honor of William Pitt, the British Prime Minister, who had proven to be a friend to the Scots. "