The bridge was built in 1638 (the date is on the downstream side) and has since been widened and extended. It is called Y Bont Fawr (the Big Bridge) to distinguish it from a smaller bridge that lay just to the south.
Dolgellau has suffered from many floods. One major flood in 1903 destroyed part of the bridge. The top end of Bont Fawr was raised to accommodate the railway which ran on the line of the present bypass. The station was just upstream of the bridge.
Initially (1868) through-passengers were obliged to change as two rival railway companies, each with its own terminus, met here. The journey from London took eight and a half hours in the 1870s. By the 1930s it was down to five and a half hours, a journey time it would be hard to equal by today's public transport.