Cwmbrân Tunnel, Pontrhydyrun
This is one of only two tunnels on the navigable part of the Monmouthshire & Brecon Canal. The other is Ashford tunnel, in Powys. The original Monmouthshire Canal also passed through a tunnel in Newport, now derelict.
Cwmbrân Tunnel is 80 metres (87 yards) long and was excavated c.1793/94. The boats were hauled by horses throughout the canal’s history as a freight transport artery. There’s no towpath for the horses to walk through the tunnel here, so how did the boats proceed against the flow of water (which was towards Newport)?
The solution was human power! Two men, one each side, placed their backs against the boat and used their feet to push against the tunnel walls. They “walked” the boat through the tunnel – a technique known as “legging” (as pictured on a different canal). The horse would walk over the hill to resume hauling the boat beyond the tunnel.
A stone at the top of the southern tunnel portal has deep grooves, which were eroded by countless towropes. Such grooves are commonly seen on the abutments of bridges where the canal turns – as at Pontymoile – but it is thought that this is the only tunnel mouth with rope grooves at its top.
It appears that the horse would continue to pull on the towrope while it walked along the towpath above the tunnel. This would have given the boat maximum momentum before the rope was unhitched and the leggers set to work.