river and estuary in eastern Scotland, flowing from west to east from its headwaters on the eastern slopes of Ben Lomond to the Firth of Forth (the estuary), near Kincardine. The river has a short highland section and a longer lowland section, falling only 80 feet (25 m) in 55 miles (90 km). This stretch, called the Links of Forth, was the site of the famous Battle of Bannockburn (Bannockburn, Battle of), fought in 1314, during which English troops suffered a major defeat at Scottish hands. Near its tidal limit at Stirling, the Forth receives two important left-bank tributaries, the Allan and Teith. The Forth–Clyde Canal, completed in 1790, is now disused.

The firth stretches for 48 miles (77 km) from Kincardine (bridged in 1936) to the Isle of May, with a constriction at North and South Queensferry, which is spanned by the railway Forth Bridge (1890) and the Forth Road Bridge (1964).