The development of quays along the Seiont waterfront was a direct repsonse to the increase in slate quarrying and the need for transhipment to export by sea transport. An Act of Parliament in 1783 provided for harbour improvements and was followed by another act in 1809. The Slate Quay, extending as far as the Union Ironworks, was developed by the Caernarvon Harbour Trust, whose office were built alongside in 1840. Investment in a dedicated slate port was consolidated by the arrival of the Nantile railway, a enterprise supported by several slate quarry proprietors. The railway was completed in 1828 and the quay subsequently served as a export point for these independant quarries. A discrete area was also set aside and subdivided into smaller plots to serve as copper ore and coal yards.

Sources include:
Cadw, 2010, Caernarfon Waterfront: Understanding Urban Character

Maritime Officer, RCAHMW, February 2013.