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Under the Saint-Martin-de-Corleans district of Aosta lies a prehistoric sanctuary of around 10,0001 square meters, dug out 6 meters below the modern street level and in use from the late Neolithic to the early Bronze Age.
6 meters down, below the modern street
The excavated area covers around 10,0001 square meters and sits 6 meters below the level of the road above it.
It was a sanctuary, in use from the last centuries of the 5th millennium BC through the early Bronze Age, then again in Roman times and in the Middle Ages. What came out of the ground is a ritual landscape: anthropomorphic stelae, ritual pits, alignments of wooden posts, dolmen tombs and cist burials.
The stelae are the part people remember. They are carved slabs with a human figure on them, standing in rows, and they were already old when the Romans arrived.
The building above is engineered around the hole
The museum over the site covers 9,8201 square meters and clears 46.51 meters in a single span.
That span is the point of the design. Nothing rests on the excavation, so the sanctuary can be read as one continuous surface rather than as trenches between pillars, which is how most urban digs end up being displayed.
Three dates, one museum: 2016, 2023, 2025
The museum was inaugurated on June 24, 2016, reopened in November 2023 and took the name MegaMuseo in February 2025.
Three names for the same address in nine years is worth knowing before you search for it. Older guidebooks call it the area megalitica di Saint-Martin-de-Corléans, more recent ones the MegaMuseo, and both are the same place.
Here is the gap we could not close: hours and ticket prices are not published on any page we could read on valledaostaheritage.com. That is unusual for a site of this size, and it means you check locally rather than plan around a published timetable.
25 BC: a Roman colony dropped on top
Aosta was founded in 25 BC as Augusta Praetoria Salassorum, and its walls enclosed 414,1282 square meters with 4 gates.
One of those gates, the Porta Praetoria, is still standing. So are the Roman theater, the forum cryptoporticus, the Roman bridge and the Arch of Augustus. The regional source describes the city as holding more visible Roman remains than anywhere in Italy except Rome, which is a popular formula rather than a measured ranking, and is worth treating as such.
The two things sit on the same ground. A colony was laid out in 25 BC over a sanctuary whose last use, in the early Bronze Age, was already ancient history by then.
The Arch of Augustus argues with itself
The arch was raised in 25 BC for the victory over the Salassi won by Aulus Terentius Varro Murena, and its single opening measures 11.403 meters under the keystone.
Look at how it is put together and you find 10 half-columns with Corinthian capitals holding up a Doric entablature with metopes and triglyphs. Those two orders do not belong together in a textbook, and here they do.
It is the same year as the city walls, the same campaign, and the same military logic: build fast, build large, and let the details argue.
What to read the site as
The sequence is the story: a sanctuary in use before 4000 BC, a Roman colony in 25 BC, a medieval town, and a modern district that put a road over all of it until the excavations went 6 meters down.
Nothing about the surface of Aosta tells you the sanctuary is there, and that is the whole reason it survived: a district built over a field, and a field that turned out to be a cemetery and a temple.
Read in that order, the 25 BC colony stops being the oldest thing in Aosta and becomes the middle chapter. The sanctuary was already out of use when the legions arrived, the Middle Ages built over it again, and only the excavation put the sequence back in view.
It also explains the shape of the visit. Roman Aosta is on the surface and you meet it by walking; the megalithic area is a single room you go down into, and the 46.51 meter span overhead is what lets you see it whole. For the wider region, see Valle d'Aosta.