Ashford Tunnel is 375 yds (343m) long and is situated one mile south of Talybont-on-Usk, alongside the B4558. It is the only tunnel on the Brecknock and Abergavenny Canal (NPRN 85124) and is constructed of a portal of sandstone rubble with a stone keystone and brick voussoirs to the round arched entrance. The tunnel has one ventilation shaft, and is of cut-and-cover construction. In normal circumstances an open cutting would have been used but the ground was so unstable that a tunnel was substituted. There is a parapet to the roadside which partly overlaps the east side of the arch. The canal towpath does not continue through the tunnel, the boats were shafted through. The tunnel re-opened after repair 1985.

RCAHMW, 14 July 2011

Sources:
Cadw listed buildings database.
A Guide to the Industrial Archaeology of South East Wales, AIA, 2003