Two studies published in 2025 push the story of exchange around the Gulf of Papua back about three thousand years: sea shells carried 200 kilometres inland up the rivers, and Lapita pottery on a beach that is now dry land.
Our Thousand-Pot Voyage tells how Motu sailors carried clay pots west across the Gulf to trade for delta sago. Archaeologists now think that voyage was the late chapter of a far older story, one that ran up the rivers as well as along the coast.
High on the limestone plateau whose rivers feed the Gulf, a cave floor holds small sea shells, threaded and worn, from about 3,250 years ago.
Walufeni Cave sits at the eastern end of the Great Papuan Plateau in Southern Highlands Province, about 200 kilometres in a straight line from the south coast. The plateau is a limestone karst country of more than 2,000 square kilometres, drained by the Kikori and Hegigio to the north and by the Turama, Bamu and Wawoi to the south. All of them empty into the Gulf of Papua.
Excavations by Bryce Barker, Lara Lamb, Teppsy Beni and colleagues recovered the remains of at least 61 marine shells. Almost all are small dog whelks (Nassarius, 54 individuals), with four olive shells and three cowries. Every one had been modified for use. Some of the dog whelks still carry traces of red pigment or resin, and the olive shells had their tips removed so they could be threaded. Across New Guinea, shells like these are sewn onto bags, masks and chest ornaments.
The shells appear suddenly, from about 3,250 years ago. The team's earlier report on the cave, in 2023, also noted that marine shell is missing from the later layers of the sequence.
The authors link the shells to the spread of Austronesian influences along the south coast of Papua New Guinea and into Torres Strait, a network the archaeologist Ian McNiven calls the Coral Sea Cultural Interaction Sphere. Usually pictured as a maritime system, it here reaches inland by river. The authors also connect the shells to the arrival of the ancestors of the Kasua people on the plateau, a movement remembered in Kasua oral tradition and supported by language studies.
East along the coast, a village site now well inland held a handful of sherds that tie the south coast to the wider Lapita world.
Lapita pottery, decorated by pressing a toothed tool into wet clay, first appears in the Bismarck Archipelago about 3,300 years ago. For a long time it was thought to be absent from mainland New Guinea, until salvage excavations at Caution Bay, near Port Moresby, in 2009–2010 found the first stratified mainland Lapita sites, about 2,900 years old.
The Gulf of Papua already has one Late Lapita site: Hopo, on a former beach line now inland, with dentate-stamped pottery about 2,600 years old. In 2025 Robert Skelly, Glenn Summerhayes, Ian McNiven, Bruno David and colleagues added another to the south coast.
Giligilina is an ancestral village on the Aroma coast, 160–180 kilometres southeast of Caution Bay. As rivers brought sediment down and the coast built outward, the site was left 3.2 kilometres inland. Its small pottery assemblage, dated to between 2,660 and 2,420 years ago, includes three dentate-stamped sherds and two with distinctive shell-impressed decoration. Similar shell impressions occur on pottery from Kaveharo and Hohelavi, beside Hopo in the Gulf.
The authors read Giligilina as evidence of busy Late Lapita seafaring, with people carrying pots or pot-making knowledge west into Torres Strait and south along the Australian coast, in a period of change that eventually ended recognisable Lapita decoration.
Read together, the two studies describe a Gulf that was connected long before the voyages of the lakatoi. Shells moved inland along the Kikori and its neighbours; pottery traditions moved along the coast. In the authors' words, these networks culminated over many centuries in the Motu Hiri trade in pottery and shell ornaments for sago that ethnographers recorded.
That is also a reminder of what the rivers mean here. The five great rivers on our home page are not only water and silt. For thousands of years they have also been roads.
Marine shells, mostly small dog whelks (Nassarius), with a few olive and cowrie shells, all modified for use. The earliest date to about 3,250 years ago, in a cave about 200 km in a straight line from the south coast.
At the eastern end of the Great Papuan Plateau in Southern Highlands Province, Papua New Guinea. Rivers from the plateau, including the Kikori and Turama, drain into the Gulf of Papua.
An ancestral village site on the Aroma coast of Papua New Guinea's south coast, now 3.2 km inland, where Late Lapita pottery dated to between 2,660 and 2,420 years ago was found.
The authors place them in long-distance coastal networks that, over many centuries, culminated in the Motu Hiri trade of pots and shell for sago recorded by ethnographers.
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