A roving bridge is a bridge over a canal constructed to allow a horse towing a boat to cross the canal when the towpath changes sides.
The Roving Bridge at Hampstead Road Locks was built in 1846. It dates from the first phase of expansion of the Goods Depot, when the railway company established its own interchange facility. The alignment was dictated by the positions of the docks that had been created in 1816 on the north and south sides. The towpath was diverted to the south side at Hampstead Road Locks before regaining the north bank on the opposite side of the Hampstead Road (now Chalk Farm Road).
The bridge was manufactured in Newport, Monmouthshire by Joseph Deeley’s London and Newport Iron Works. As well as an iron founder, Deeley was an engineer and an inventor, having developed a patent foundry furnace that allowed iron to be smelted using a cleaner and less costly process, resulting in both a higher yield and a superior quality of iron.
The bridge is formed as a distinctive cast iron arch cum vierendeel truss, a rare example of a cast iron arch bridge with wrought iron tie bars fixed at the top of the parapet (Malcolm Tucker). No other cast iron towing path bridges with these have been identified. The tie bars carry the tensile loads and induce a state of permanent compression in the lower flanges in the same way as in a post tensioned concrete beam.
The clear span of the bridge is 79’-6” (24.25 m) with a rise 4’-0” (1.20 m). The parapets are at 7’ 3” (2.21 m) centres.
It is cast in four pieces. Each side of the bridge consists of two halves, joined at the centre with two hexagonal bolts. At the ends of the bridge the top rails swell into massive blocks, with large cylindrical anchorage lugs cast integrally, each of which carries two 11/4” (32 mm) diameter steel tie bars. Originally of wrought iron they run from the top of the bridge, but the curvature carries them down to below the footpath at the centre.
The Regent’s Canal Company decided in mid-1846, after the Roving Bridge had been completed, to provide horses for towing. The stabling at Hampstead Road Locks provided stalls for up to 18 horses. Barges in the southern lock had to be towed across to the northern bank to continue their journey.
The rope would pass under the Roving Bridge on the upstream side to be attached to the horse, now on the bridge. The horse then pulled the barge across to the other bank. The force on the rope required to turn the barge against the flow of canal water was so great that the parapet rail of the bridge and the stone parapet of the abutments are deeply scored, evidence of past operations.
