The town's name comes from the old fort built here in 1654 by General Monck during the Cromwellian occupation, rebuilt in stone in 1690 and named for William of Orange. It saw action in both Jacobite risings, surviving a famous Jacobite siege in 1746. After the railway arrived in 1894, most of the fort was demolished to make way for the station, but a stretch of curtain wall, the river bastion, and parts of the entrance gate still stand on the shoreline below the railway.
The remains are open to the public, with information boards explaining the layout. A short, scrappy walk from the town centre — not a great sight in itself, but the reason Fort William is here at all.