The discovery in 2010 of stratified Lapita assemblages at Caution Bay near Port Moresby, south coast of mainland Papua New Guinea (PNG) (David et al. 2011; McNiven et al. 2011), brought to the fore a series of important questions (Richards et al. 2016), many of which also apply to other parts of Island Melanesia where Lapita sites have been known for many decades. Unlike other parts of Melanesia, however, at Caution Bay some of the Lapita sites also have pre-Lapita horizons. A number are culturally very rich. At Caution Bay, where the oldest confirmed Lapita finds date to no earlier than c. 2900 cal BP (McNiven et al. 2012a), the major questions do not concern the earliest expressions of Lapita around 3300–3400 cal BP. Rather, here we are concerned more with identifying how assemblages associated with the Lapita cultural complex arrived and transformed along the south coast, after a presence in coastal and island regions to the northeast over the previous 400 years. These concerns contain both spatial and temporal elements: how and when, as a prelude to why, particular cultural traits continued and changed across Caution Bay. Tanamu 1 is the first of 122 archaeological sites excavated in Caution Bay upon which we will report. As a site, it represents the ideal entry point, as being a coastal site which contains pre-Lapita, Lapita and post-Lapita horizons it encapsulates many of the signatures, trends and transformations seen across the >5000 year Caution Bay sequence at large. Of special note in the wider context of Lapita archaeology, the presence of rich pre-Lapita horizons is what makes Caution Bay so important both in and of itself and for the Lapita story.