The royal tombs of the ancient Tongan state (1250–1800 CE) are the largest set of monumental funerary structures in the Pacific. The tombs were built with stone facings made by quarrying slabs of beach rock from the intertidal zone and transporting the worked stone to the central place of Lapaha. Conservation of five royal tombs to reset damaged facings documented aspects of the construction process and the dimensions of more than 700 slabs. This paper outlines the quarrying, transport, and use of worked beach rock in the mortuary structures of the paramount Tu’i Tonga dynasty. Slab dimensions indicate that tombs were planned structures with larger slabs consistently found in the basal west wall and smaller slabs found in upper tiers of stone work. Measurements suggest that slab length was highly variable compared with height/width with no evidence for extraction of a “standardized” slab. Variability in slab dimensions likely results from natural variation in beach rock exposures, the use of large slabs to manifest chiefly support, and size change caused by fitting and finishing slabs. Analysis of stone working practices in Oceania contributes to knowledge of prehistoric architecture and whether or not ancient masonry techniques were dispersed anciently by voyaging and culture contact.