The Treveneague fogou was discovered in 1866 during ploughing, when the entrance to an underground passage was revealed in a field near the eastern ditch of what is now recognised as a round. The ditch was about nine feet deep and could be traced on three sides, although the northern side had already been damaged by quarrying and the bank had been levelled before the site was recorded. The first excavation took place soon after discovery, but the most detailed early account came from Henderson, who investigated the site between 1914 and 1917. Henderson recorded the blocked entrance at around SW 54783301 and noted that changes in field boundaries had made earlier attempts to relocate the site difficult. His work showed that the fogou belonged within a wider enclosed settlement landscape rather than standing alone. Like other Cornish fogous, it was a subterranean structure associated with an Iron Age or Romano British round, though its exact original purpose remains uncertain. The architecture of the Treveneague fogou shares similarities with examples at Chapel Euny and Pendeen Vau. It included an arched chamber rather than a corbelled one, and the chamber had been cut directly into solid clay. The passage floor contained a thick greasy layer of mould, which produced charcoal, animal and bird bones, a granite saddle quern, and an iron bill hook of La Tène type. Possible human remains were also reported, although the evidence for this was never secure. Pottery from the fogou added to the importance of the site. A bowl of black polished ware was reconstructed from sherds found inside the passage, and its style closely resembled Iron Age Glastonbury ware. Similar sherds were found in the surrounding ditch. Henderson also recovered seventeen pottery types, flint implements, two querns, and further iron objects. Later disturbance produced fragments of medieval pottery, suggesting that the area may have been reused or visited long after the fogou’s original period of use. In 1995, the site was re examined by Time Team using geophysical survey and excavation directed by Tim Taylor. This work successfully relocated the fogou and confirmed it as an Iron Age feature. The survey also identified a curving ditch anomaly, supporting the idea that the fogou lay within a larger enclosure or round.