The Zion Congregational Church was founded, and the first chapel built, in 1824. In 1878 this chapel was demolished and replaced with a building 20ft longer, and designed by notable architect John Humphrey of Morriston, using a similar design to that of Tabernacle, Morriston. Materials and construction of the new chapel cost £1,550 and increased seating from 308 (1851 Religious Census) to 500 (Royal Commission on the Church of England and other Religious Bodies).
The chapel is built in an Italianate Classical Renaissance style, the 'Temple' facade dominated by with giant Corinthian columns rising to support three semi-circular ‘triumphal’ arches above the level of the gallery windows.' Above this is a gabled pediment with raked modillion cornices and a circular opening with inset circlets providing ventilation to the roof space. Steps lead to an entrance in each of the three bays created by the columns, the central doorway leading to the main vestibule, the outer doorways leading to the gallery staircases. Above the doorways, a mezzanine story is punctuated by a series of window slits, over which runs a plain cornice, inscribed with the the inscription "Founded AD 1826; Zion Congregational Chapel; Rebuilt 1878". Above are tall, round-headed gallery windows with Italinate glazing. The column bases either side of the central doorway are set with foundation stones dated to June 14th, 1878. The whole is constructed from bull nosed rubble with freestone columns and dressings and it set to the rear of a long, grassed, forecourt enclosed with brick walls with cast-iron railings.
The interior, which was altered slightly in the 1960's, is entered via the central vestibule, which has a stained galss window on to the main auditorium by Maile & Son Ltd, Bayham Street, London. this depsictes 'The Good Samaritan' and 'Suffer the little children' and is dedicated to Thomas Wilfred Benbow (died 1963). The auditorium has a raked floor with three blocks of seating set on a continuous curve, similar to The Rev. Thomas Thomas's Capel Seion, Llandysul of 1870-71. the open bech pews have numbered ends. The original Sedd Fawr enclosure has been removed to provide an open platform, from whcih leade a set of steps to either side of the central pulpit - the balustrades to these, and the decoration to the front of the pulpit, mirror the columned arches of the facade. The four-sided gallery is supported on seven cast-iron columns with foliage caps, and the gallery front is inset with openwork cast-iron panels. the rear gallery front, facing the pulpit, is inset with a clock lableed 'Wm edwards, Llanidloes'. The north-east end (above the pulpit) contains an (inserted?) pipe organ by Wadsworth &Br, Manchester, supplemented by a modern piano and electric keyboard to the ground floor. There is a rare example of a hollow eighteenth century bureau, claimed as a place in which priests were able to hide. There are a number of wall memorials
A red brick school room was built to the rear of the chapel in 1932.
The chapel is now Grade II* Listed because of its 'specially important façade', and in 2004 the name was changed to Trinity Chapel to reflect the merger of Bethel Street English Presbyterian Church with Zion URC.
RCAHMW, May 2020
Ref: Cadw Listing Description 3871
RCAHMW Site Visit March 1997