Fort Ticonderoga, formerly Fort Carillon, is a large 18th-century star fort built by the French at a narrows near the south end of Lake Champlain in northern New York in the United States. It was constructed by Canadian-born French military engineer Michel Chartier de Lotbinière, Marquis de Lotbinière between October 1755 and 1757 during the Seven Years' War, often referred to as the French and Indian War in the US. It was of strategic importance during the 18th-century colonial conflicts between Great Britain and France, and again played an important role during the American Revolutionary War.
The site controlled a river portage alongside the mouth of the rapids-infested La Chute River in the 3.5 miles (5.6 km) between Lake Champlain and Lake George and was strategically placed in conflicts over trade routes between the British-controlled Hudson River Valley and the French-controlled Saint Lawrence River Valley. The terrain amplified the importance of the site. Both lakes were long and narrow, oriented north–south, as were the many ridge lines of the Appalachian Mountains extending as far south as Georgia, creating the near-impassable mountainous terrains to the east and west of the Great Appalachian Valley that the site commanded. The name "Ticonderoga" comes from the Iroquois word tekontaró:ken, meaning "it is at the junction of two waterways".
During the 1758 Battle of Carillon, 4,000 French defenders were able to repel an attack by 16,000 British troops near the fort. In 1759, the British returned and drove a token French garrison from the fort merely by occupying high ground that threatened the fort. During the American Revolutionary War, the fort again saw action in May 1775 when the Green Mountain Boys and other state militia under the command of Ethan Allen and Benedict Arnold captured it in a surprise attack. Cannons captured were transported to Boston where their deployment forced the British to abandon the city in March 1776. The Americans held the fort until June 1777, when British forces under General John Burgoyne again occupied high ground above it and threatened the Continental Army troops, leading them to withdraw from the fort and its surrounding defenses. The only direct attack on the fort took place in September 1777, when John Brown led 500 Americans in an unsuccessful attempt to capture the fort from about 100 British defenders.
The British abandoned the fort after the failure of the Saratoga campaign, and it ceased to be of military value after 1781. It fell into ruin, leading people to strip it of some of its usable stone, metal, and woodwork. It became a stop on tourist routes of the area in the 19th century. Its private owners restored the fort early in the 20th century. A foundation now operates the fort as a tourist attraction, museum, and research center.