In Roman times the Bruckneudorf area was already densely populated, and Villa Bruckneudorf, one of the most important Roman villas to be discovered in Eastern Austria, is a few kilometres to the east. The villa is presumed to be a residence of the imperial family in the autumn of 375 AD. Today impressive ruins remain. Of the magnificent mosaics, more than 300 m² are still preserved. These are located in the Landesmuseum in Eisenstadt.
Sirmione castle was built near the end of the 12th century as part of a defensive network surrounding Verona. The castle was maintained and extended first as part of the Veronese protection against their rivals in Milan and later under the control of the Venetian inland empire. The massive fortress is totally surrounded by water and has an inner porch which houses a Roman and Medieval lapidary. From the drawbridge, a staircase leads to the walkways above the walls, providing a marvellous view of the harbour that once sheltered the Scaliger fleet. The doors were fitted with a variety of locking systems, including a drawbridge for horses, carriages and pedestrians, a metal grate and, more recently, double hinged doors. Venice conquered Sirmione in 1405, immediately adopting provisions to render the fortress even more secure, fortifying its outer walls and widening the harbour.
Thanks to its strategical geographical location as a border outpost, Sirmione became a crucial defence and control garrison for the ruling nobles, retaining this function until the 16th century, when its role was taken up by Peschiera del Garda.