Ratau is large pa that forms part of the dense archaeological landscape of the Tolaga Bay (Uawa) area. It is located on the high point of a major east-west running ridgeline on Mangaheia Station, west of Tolaga Bay.

Ratau is one of the numerous pa that have been recorded in the Tolaga Bay area, mostly located on the prominent hills and ridgelines which afforded excellent natural defences and provided commanding views of the surrounding landscape. These pa and the many other archaeological sites recorded in the Uawa region such as pit and terrace complexes, midden, gardens and urupa reflect the intensive occupation of this landscape by Maori from the time of initial Polynesian settlement approximately 700 years ago. Access to abundant food resources from the sea, rivers, inland forests and horticultural production (kumara) meant that a large population could be sustained. It has been estimated that the early Maori population of Tolaga Bay totalled approximately 1200; and the main iwi was Te Aitanga a Hauiti.

Ratau is believed to have been occupied by the iwi known as 'Tarewa', who were subsequently overthrown by a neighbouring Mangaheia Valley iwi. The descendants of this Mangaheia Valley iwi were later known as 'Hingaroa'. The name Ratau means 'last hill to catch the sun at the end of the day'. The approximate date/period of Tarewa's occupation of Ratau is unclear.

Ratau is located in pasture on the peak of a major east-west running ridgeline approximately 1.3 kilometres west of Mangaheia Road, where there is a bridge over the Patiki Stream. The pa mostly occupies the very narrow, steep-sided ridge crest, extending for a length of approximately 200-220 metres, and it is generally no more than 8 metres in width. It possesses both natural and artificial defences. Pit site Y17/167 is located immediately to the northwest of the pa (and is considered to be associated with it) and there are a number of other recorded archaeological sites in the surrounding area.

This pa was first recorded by archaeologist Kevin Jones during his archaeological survey work in the Whangara, Tolaga Bay and Uawa Catchment areas in 1982-1983. This survey work was undertaken to gain information about the nature of prehistoric settlement in this locality, and also to evaluate specific sites for registration under the Historic Places Act 1980. Jones described the site as 'a ridge pa some 200m long with strong natural defences' and later estimated that it could have sustained a population of approximately 167 individuals. An artificial defence in the form of a double ditch and bank cut across the principal ridge of the pa, dividing it into 'east and west'. A number of pits were also recorded within the pa, particularly along the ridge running down to the northwest from the principal ridgeline. With regards to the condition of the pa, stock damage was noted as an issue. The narrowness of the principal ridgeline meant that the site was particularly vulnerable to damage from stock moving along the ridge crest.

Ratau was revisited by archaeologist Bridget Mosley in 2000 as part of the New Zealand Archaeological Association Site Recording Scheme Upgrade Project. Mosley noted that the pa was significantly eroded at its eastern and western ends, and in average condition overall. The erosion meant that features such as the double ditch and bank were difficult to re-identify.

A slip was observed at the south-western end of Ratau during a New Zealand Historic Places Trust site visit in November 2007, but no other major changes were noted.

Ratau is one of the numerous pa recorded in the Tolaga Bay area, particularly in the Mangaheia Valley, and it is part of a much wider archaeological and cultural landscape that is of considerable significance to Te Aitanga a Hauiti. This landscape reflects the intensive Maori occupation and settlement of the Tolaga Bay area since the 14th - 15th centuries AD.