The Castle of Osma is a medieval castle which seems to have been built in the 10th century. It was built in stone, although Count Gonzalo Tello used some Roman structures and materials which belonged to a small Christian fortress.
The castle is divided into three walled enclosures which can be easily distinguished. Nowadays you can see the ruins of this fortress which adapts perfectly to the rocky hill between the Ucero and Abión rivers, near the famous Roman city of Uxama. It was used mainly as a defensive structure located in the natural passageway to this valley and the City of Osma. Some of the walls of the main enclosure are still standing which help to make out the floor plan and you can still see its Keep, remains of other towers, the access gate and a small door. There are also remains of the other two enclosures that improved the castle’s protection. On the outer wall that goes down the hillside, you can see the Water Tower (Torre del Agua) that is located near the river.
The Castle of Osma has experienced many battles from its first reconquest in 912 all the way up to the last in 1088, and in the 15th century, it belonged to the bishop of Osma.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.