Grota do Medo

The Grota do Medo Megalithic Complex occupies a wooded slope in the parish of Posto Santo, in the central highlands of Terceira a few kilometres north of the city of Angra do Heroísmo. The site sits at roughly forty-five metres above sea level on the hill known locally as Pico do Espigão, with sight-lines to the southern coast, to inland watercourses, and to the higher peaks of the island interior. The surrounding parish takes its name from the bubonic plague outbreak of 1599, when the area was spared and served as a refuge for residents of Angra. The megalithic structures themselves predate that history by an order of magnitude and are not referenced in any Portuguese cadastral or historical record of the parish.

The site was brought to academic attention by António Félix Rodrigues, a researcher at the University of the Azores, who first presented it at the 16th Annual Mediterranean Studies Association International Congress, held in Angra do Heroísmo in May 2013. Rodrigues subsequently published a detailed description in 2015 in the journal *Archaeological Discovery* under the title "Megalithic Constructions Discovered in the Azores, Portugal". An earlier 2012 survey paper by Antonieta Costa of the CITCEM research centre at the University of Porto had already listed the location as one of four anomalous archaeological areas on Terceira, alongside the Mount Brasil hypogea, the cart ruts of São Brás, and a separate complex of stone constructions at Serreta.

Rodrigues documents two principal classes of structure on the site. The first class, identified as comparable to Atlantic-façade passage tombs of the type found from western Scotland to southern Spain, consists of a corridor running approximately four metres into a mound, terminating in a circular space roughly three metres across that is interpreted as a collapsed burial chamber. Two such structures occur on the hillside, one positioned approximately ten metres above the other, both with entrances oriented to the southeast. The second class, comparable to Irish portal tombs, consists of four structures with east-facing entrances, rectangular or trapezoidal chambers, roofs constructed by a process resembling corbelling, and surrounding dry-stone walls incorporating orthostats. The largest of these stands over 1.5 metres in height with paired capstones each over three metres long, set at an angle close to ninety degrees.

Across the complex, capstones and outcrops carry dozens of carved bowls, or cup-marks, comparable to the bullauns documented in Ireland and Scotland and to similar features on the Swedish island of Gotland and in Lithuania. The bowls retain water during rainfall, which then drains in defined channels toward the cliffs and toward the entrances of the tomb-like structures. Surrounding the chambers, Rodrigues records cut-marks on trachyte rock comparable in shape and volume to those documented at megalithic quarries in France, Ireland, Portugal, and Malta. A number of stones bear inscriptions and figurative engravings, some of which Rodrigues and later authors have compared to Libyco-Berber rock art of North Africa.

In a follow-up study published with Nuno Martins, Nuno Ribeiro, and Anabela Joaquinito under the title "Early Atlantic Navigation: Pre-Portuguese Presence in the Azores Islands", a man-made rock basin from the site was submitted for Accelerator Mass Spectrometry dating. The result indicated human activity at or before the eleventh century, well in advance of the official Portuguese discovery and settlement of the archipelago, conventionally dated to 1427 under Prince Henry the Navigator. The authors note that the dating establishes a pre-Portuguese human presence on Terceira but does not, in the absence of artefacts, identify the culture responsible.

The interpretation remains academically contested. Portuguese mainstream historiography continues to treat the archipelago as uninhabited before the fifteenth century, on the basis of contemporary Portuguese sources that describe the islands as empty on first arrival. The structures at Grota do Medo, together with the hypogea documented at Mount Brasil by Nuno Ribeiro and Anabela Joaquinito, sit outside that orthodox account. No formal excavation has been conducted at Grota do Medo, no artefacts or pottery have been recovered, and no follow-up dating campaign has been undertaken. The site is currently accessible to the public through a private tourism operation, Ancient Azores, established to preserve and present the complex while academic debate continues.