Bridge, c.1805, possibly by John Rennie. Of red brick in Flemish bond with gritstone coping. Single span, elliptical arch, brick band, slightly splayed parapet with recessed centre panel and slightly advanced end piers. One of a series of bridges across the Cowbridge Drain, laid out when the fens were drained by John Rennie. For the full description and the legal address of this listed building please refer to the appropriate List of Buildings of Special Architectural or Historic Interest. {1} Mastin's Bridge is situated north-east of Boston and carries the C66 road over Cowbridge Drain, between Boston Long Hedges and Willoughby Hills. Four rounded stones are set into the parapet, originally intended to deflect carriage wheels. The bridge is generally in good condition though there are areas of minor defects and widespread lichen growth. Spalling has occurred on the arch and abutments and mortar loss from joints has occurred throughout the structure. Some repointing has been done on the roadside face of the parapet and at the arch crown. Water seepage can be seen on the underside of the arch. Two areas of the parapet, damaged by a vehicle collision, have been repaired in the past with common bricks. {2}{3} Adjacent to the bridge there is a large buried brick chamber on the south side of Cowbridge Drain that appears to be contemporary with the bridge. The local drainage engineers have noted that it is unusual and do not know of another like it. It is at the end of a drain just before it flows into Cowbridge Drain. It may well be a water baffle with the sunken chamber floor perhaps used for collecting dense (none floating) debris. It would not necessarily stop sediment from being washed though. A baffle just before the culvert outfall into Cowbridge Drain (some 25m immediately to the north) would make sense, especially if subject to high flow as it would be from time to time, so as to regulate any discharge and not encourage bank erosion at the outfall in close proximity to the bridge abutment. It seems to be more than 60m long more than a metre wide and more than two metres high. {4}