At the time of the Austro-Hungarian Empire and following its cession to Italy after the First World War, a series of archaeological excavations were carried out in Grado, resulting in the identification of the Castrum. Recent investigations and detailed studies by the Office of Archaeological Heritage of Friuli Venezia Giulia made it possible to date its construction back to the first half of the 6th century AD. On the basis of mediaeval literary sources, however, some local expert historians believe it dates back as far as the early 5th century.
The late antiquity fortified settlement stood out for its unusual “sandal sole” shape, and was built with impressive walls that were 9 to 10 Roman feet thick, or just under 3 metres. The foundations are at a depth of approximately 2.5 metres below today’s ground level, and parts of the walls can still be traced in some points of the picturesque, ancient town centre, covered over time by houses, courts (campi), squares (campielli) and alleys (calli). The town wall was made from small, even blocks of sandstone set with mortar. It was approximately 5-6 metres high, 360 metres long and 50 metres wide to the north and over 90 to the south. It appears to have had nine rectangular and polygonal towers, as can be made out in Campo Porta Nuova. Only traces remain of just two of the six city gates, in the east and southwest. The western boundary of the Castrum coincides precisely with today’s Piazza Duca d’Aosta and Via Gradenigo: in fact, the local name for the neighbourhood next to the former church of St. Rocco is “de fora”, meaning outside, whereas today’s Calle del Palazzo and Calle Lunga appear to follow the original axis inside the walls.
Although its main purpose had naturally been that of defence, the construction of the fortified perimeter and the increased number of buildings inside the walls are signs of fundamental socioeconomic, political-military and, last but not least, religious changes. The definite development and rapid rise in importance of Gradus – hence its name, signifying a ‘step’, a ‘port of call’, a ‘landing place’ on the open sea – contributed to it becoming a true urban centre. This was the outcome of its main purpose to act as a river port for Aquileia, which had been founded in 181 BC with an immense river port, but was destroyed by Attila’s Huns in 452 AD. As a result of Attila’s destruction of the Roman metropolis, ancient Grado not only offered shelter to the fleeing population and clergy, but then became the seat of ecclesiastic power at the time, determined by the presence of the Bishop and subsequently that of the Patriarch of Aquileia.
From a historic viewpoint, our island can be considered as the ‘daughter’ of Aquileia and to some extent the ‘mother’ of Venice. This was not merely because legend has it that once the inhabitants of Aquileia had settled in Grado, they went on to populate the islands of the lagoon as far as ‘Rivus Altus’, the original settlement of the future city of Venice, but also because Grado was the parent of the regional capital of Veneto from an ecclesiastic viewpoint. The splendour of the Patriarchs of Grado and their great power and extensive control over vast areas of the Upper Adriatic at the time of the Byzantine rule lasted until the latter’s decline. Venice then became a continually expanding religious centre, even though it remained under the Patriarch of Grado until the 12th century, when the Patriarch moved his residence there and only returned to Grado on special occasions. The papal bull of 1451 put an end to the tradition of Patriarchs in Grado and the figure of the Patriarch of Venice replaced them.
In order to imagine a more vivid picture of the Castrum, we suggest you enter the impressive Basilica of Saint Eufemia and go up to the high altar: the modern floor mosaic below it gives a stylised, yet effective portrayal!