At some 55 miles (88 km) in length, with a maximum width of 19 miles (31 km) at its mouth, the Firth of Forth represents the most substantial estuary on the east coast of Scotland. The Firth can be said to begin at Stirling, its tidal limit but where it can be easily crossed, and then enters a series of meanders before beginning to broaden just to the south of Alloa. To the southeast is the Clackmannan Bridge (2008), the first of four which cross the Firth. Almost immediately thereafter comes the Kincardine Bridge (1936). The river then turns east, flowing between Grangemouth and Culross, and on through the Queensferry narrows, where it is crossed first by the Forth Road Bridge, a sleek suspension bridge opened in 1964, and then the world-renowned Victorian super-structure of the Forth Rail Bridge. Thereafter the Firth widens markedly as it passes Edinburgh, but narrows again between North Berwick and Elie Ness, before widening once again and flowing out into the North Sea between Dunbar and Fife Ness. The Firth contains several small islands, the more significant of which are the Bass Rock, Cramond, Craigleith, Eyebroughy, Fidra, Inchcolm, Inchgarvie, Inchkeith, Inchmickery, Lamb and, farthest out, the Isle of May.
Perhaps the most spectacular sight came in 1918, when the entire British Grand Fleet, together with representative ships from the other allied powers, some 201 warships in total, assembled at the mouth of the Firth to meet the Imperial German High Seas Fleet (a further 70 ships) en route to internment.
The Firth remains an important communication route, with shipping serving significant ports at Alloa, Bo'ness, Burntisland, Grangemouth, Granton, Leith and Methil, as well as the Royal Dockyard at Rosyth, an Oil Refinery at Grangemouth, an Oil Terminal at Hound Point and numerous small harbours with a few fishing boats or a larger number of yachts often berthed in one of several marinas.