1999:192 - DUBLIN: City Hall, Cork Hill, Dublin

The City Hall was built originally as the Royal Exchange by the merchants of Dublin to the design of architect Thomas Cooley. Construction commenced in August 1767 and was completed in 1779. The Royal Exchange was subject to major alterations in 1851, when it was taken over by Dublin Corporation in order to create new offices. The last major structural alteration carried out on the City Hall to date was in 1926, when the woodwork supporting the dome was found to be badly affected by dry rot.

During the excavation for a proposed lift shaft, a blackstone wall emerged at 2.1m down from present street level (or 1.8m from first-floor level, 6.23m OD). This portion of blackstone wall extended north-south for 2.45m, and a width of 1.1m was exposed, co-linear with the north-eastern structural wall of the City Hall. The southern end of the wall had been demolished during the construction of a deep service trench; its northern end extended into the north section face.

This portion of wall remains appears to form part of the town wall that enclosed medieval Dublin. The condition of the wall was good, comprising faced regular blackstones 0.3m x 0.3m, with thinner, long slabs between them, all bonded by a yellow/white, gritty mortar.

The material excavated out for the service ducts and the overall ground reduction was uniform throughout, consisting of a brown, shell-concentrated clay with some 18th-century inclusions. It would appear that the ground had been built up to create a building surface for the construction of the Royal Exchange in 1769. This clay layer was at least 3.8m deep, as verified during the excavation for the lift ram.

The original floor level of the vaulted basement was 6.413m OD (i.e. with present street level). This floor level was reduced by 0.65m all over the basement area. The material was uniform throughout, consisting of a redeposited, brown clay infill with shell concentrations, animal bone, clay pipe stem, black- and creamware sherds and one 18th-century wig curler. A broken vertex of human skull was retrieved from the fill thrown down over an old manhole trench, at a depth of 1.8m from the existing basement level. There were no significant changes in the overall stratigraphy of the deposits excavated out for the insertion of ducts and services.

The section of blackstone wall co-linear with the internal east wall of City Hall appeared to extend onwards into its northern section, following the geographical position of the eastern side of the town wall, which extended towards present-day Parliament Street up to the now-demolished Dames Gate entrance.

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