Warfare is often considered as a key factor in the formation complex societies, but in the Pacific archaeological evidence for inter-group conflict during political centralization is rare. Most earthwork forts in Tonga are assumed to have been built in the nineteenth century when the traditional system of rulership collapsed, yet few forts on Tongatapu have been excavated or 14C dated. A fort in the chiefly center of the ancient Tongan state was mapped with theodolite and LiDAR, and excavated. Radiocarbon and traditional history indicate the fort known as the Lapaha Kolotau was made in the fourteenth century AD at the same time that chiefly architecture was being built at an unprecedented scale at the new elite center. The construction of an earthwork fort provides the first evidence that political centralization in Tonga was likely to have been contested.