Trinity Bridge is the unique triangular bridge that stands at the heart of the town of Crowland. This bridge has three stairways that converge at the top. Originally it spanned the rivers that flowed through the town, although now the rivers have been re-routed and no longer flow anywhere near the bridge. The current bridge was built between 1360 and 1390 and replaced previous wooden bridges. The earliest known mention of the bridge is by Ethelbald of Mercia in 716.

What we see today has an odd triangular design - it has three arches but is one structure - hence its name ‘˜Trinity' or three in one. This came about because it stood at the point where the River Welland divided into two streams. One led past the abbey - at the water gate on the south side of the abbey site - and the townspeople used it for sanitary and sewerage purposes. It drained into the River Nene. The main branch of the Welland meanwhile carried on northwards towards Spalding. These waterways were eventually covered over by the current street pattern. Arched over, they now serve as sewers.

Crowland would have been an important place. With its abbey acting as a landmark and attraction, Crowland thrived in the medieval period. Providing a crossing for traffic would have boosted the town's importance. In the days when travel was so difficult in the fenland, any river crossing for heavy traffic was important. King Stephen granted the town a charter in 1142, while Henry VI allowed it to hold a fair and a market in the 15th century.

The bridge at one time had a large cross at its apex. It may have been used as a platform by preaching monks and as a centre of devotion for pilgrims approaching the abbey. During the Middle Ages it had gentle slopes leading upwards - in more recent times steep steps have been substituted. Occasional outdoor religious services still take place there. The suppression of the monastery in the 16th century hit Crowland badly, economically and socially, and the population ebbed away. Later land drainage and the alteration of the river course from the 17th century onwards eventually made the Trinity Bridge redundant. Navigation of the Welland became easier for larger craft, but the town and its bridge were bypassed.