Posert Castle, also known as Šabec (Schabez) and St. Martin, is a ruined fortress near the road between Paz and Šušnjevica, in municipality of Cerovlje. The ruins of the castle depending on the name are dating back to the 11th century (St. Martin), or 16th century (Šabec), while by archeological evidence to the second half of the 14th century. The castle was vastly devastated in the Uskok War (1615–17). Between 2009 and 2014 the castle was restored. Nearby the castle there is also a small Church of St. Martin from 1367.
The castle is of irregular trapezoidal layout with rectangular angle tower. The layout broad side is faced toward north. It consists of center in the northern part, and of external fortified yard in the central and southern part. The guard tower is best preserved. It had five floors, preserved to a height of 17 metres with irregular layout, 8 metres long by 6 metres wide.
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.