The Union Chain Bridge spans the River Tweed between Horncliffe, Northumberland, England and Fishwick, Borders, Scotland. When it opened in 1820 it was the longest wrought iron suspension bridge in the world with a span of 137 metres (449 ft), and the first vehicular bridge of its type in the United Kingdom.
Although work started on the Menai Suspension Bridge first, Union Bridge was completed earlier. Today it is the oldest suspension bridge still carrying road traffic. It lies on Sustrans Route 1 and the Pennine Cycleway.
The bridge has been maintained by the Tweed Bridges Trust, since the abolition of turnpike tolls in 1883. It is a Grade I listed building and Scheduled Ancient Monument.
Before the opening of the Union Bridge, crossing the river at this point involved an eleven-mile round trip via Berwick-upon-Tweed downstream or a twenty mile trip via Coldstream upstream. (Ladykirk and Norham Bridge did not open until 1888.)