.jpg){kind=link}
Aosta was founded in 25 BC as Augusta Praetoria Salassorum, its walls enclosed 414,1281 square meters with four gates, and it holds more visible Roman remains than any Italian town except Rome.
The grid of 25 BC is the grid you walk
The colony went up in 25 BC on a rectangle of 414,1281 square meters, with four gates in the circuit wall. One of them, the Porta Praetoria, is still standing, and so are the theater, the forum cryptoporticus, the Roman bridge and the Arch of Augustus.
That concentration is the reason to stop here rather than only pass through on the way to the ski valleys. You can cross the whole Roman town on foot in under half an hour.
The arch that mixes two orders
The Arch of Augustus was raised in 25 BC for the victory over the Salassi won by Aulus Terentius Varro Murena, with a single opening 11.402 meters high to the keystone.
Look up at the decoration and you see the compromise: ten half columns with Corinthian capitals carrying a Doric entablature with metopes and triglyphs. The two orders do not normally meet, and here they do, in a garrison town on a new frontier.
Twenty-two meters of theater facade
The southern facade of the Roman theater still stands 22 meters (72 feet) high, and it is the piece of Roman Aosta you see from the furthest away. It was built a few decades after the founding of 25 BC.
Behind it the seating covered an area of 81 by 64 meters and held between 3,5003 and 4,0003 spectators. For a colony that size, that is a large building, which tells you what Rome expected the place to become.
The gate, and how far the ground has risen
The Porta Praetoria was the eastern entrance of the Roman town, built in 25 BC as a double screen of arches with a courtyard between them and two rectangular towers. The central opening is 7 meters across for carts, flanked by two passages of 2.654 meters for people on foot.
Excavations in 2012 and 2013 found the Roman paving 2.5 meters under today's street. Stand in the gate and you are standing well above the level the carts used, which is why the arches look shorter than they were built.
A sanctuary six meters under the road
The megalithic area of Saint-Martin-de-Corléans lies 6 meters below street level, under a museum building of 9,8205 square meters spanned without columns for 46.55 meters. The excavated sanctuary covers an area given as 10,0005 square meters.
People used the site from the last centuries of the fifth millennium BC to the early Bronze Age, leaving anthropomorphic stelae, ritual pits, alignments of wooden posts, dolmen tombs and cist burials. The museum opened on June 24, 2016, reopened in November 2023, and has been called the MegaMuseo since February 2025. There is more at a prehistoric sanctuary under a city and at things to do in Aosta.
Aosta, month by month
| Month | Range from low to high | High | Low | Rain days |
|---|---|---|---|---|
| Jan | 40°4°C | 28°-2°C | 12 | |
| Feb | 42°6°C | 29°-2°C | 11 | |
| Mar | 48°9°C | 35°1°C | 12 | |
| Apr | 54°12°C | 42°5°C | 13 | |
| May | 62°17°C | 49°9°C | 16 | |
| Jun | 73°23°C | 57°14°C | 17 | |
| Jul | 78°26°C | 62°17°C | 16 | |
| Aug | 78°26°C | 62°17°C | 14 | |
| Sep | 70°21°C | 55°13°C | 13 | |
| Oct | 61°16°C | 47°8°C | 13 | |
| Nov | 49°9°C | 36°2°C | 13 | |
| Dec | 41°5°C | 29°-2°C | 13 |
High and low are the mean daily maximum and minimum, in °F with °C below. Rain days are days with at least 1 mm of rain.
Averages for 1991 to 2020 from the ERA5-Land and ERA5 reanalysis (Copernicus, ECMWF), grid point at 584 m, extracted September 11, 2026. Data: Open-Meteo, CC BY 4.0.
A reanalysis is a model rebuilt from observations, not a weather station. Its values can differ from the station normals quoted in the text, most of all on the coast and in the mountains. It describes the typical month, not a forecast.