The area around Lake Orta was frequented during the Neolithic period, there are traces of these peoples all over the area and on the island itself (look in the glass door at the top of the rowing-boats slide where the public landing stages are). Great rocks in the area have cup and ring marks, Iron Age necropoleis have been found on the hills above Orta. For the lake is on the main route that, from the river Po, leads to the north and to the Alpine passes, and the island is in a strategic position along this route. In past centuries the way was often over water from south to north, linking with the lakes of Mergozzo and Maggiore.
The Romans used the land route, passing through the villages above the eastern side of the lake, this way becoming during the Middle Ages the Via Francisca and defended with castles, towers and fortresses erected along the way. The island castle was an important defense, along with the castle of Pella on one side and the tower of Orta on the other, besides being a perfect refuge from warring invaders, not, presumably, furnished with boats.
That St Giulio insisted on Christianising the island probably signifies that it was in his time a place of pagan cult: Celtic, and even, perhaps, after the arrival of the Romans, Mythraic.