Built on the remains of a Roman Arx during the Lombard era, the Caiazzo Castle was owned by notable figures like Count Theodoric of Caiazzo (9th century) and Count Landone (1034). Later, it fell under Norman rule and was fortified by Roger II with permanent garrisons.
In 1229, during the Hohenstaufen period, Caiazzo was besieged by John of Brienne but was freed by Emperor Frederick II, who stayed at the castle. Under the Angevins, it changed hands multiple times, eventually belonging to Lucrezia d'Alagno in 1461, who reinforced the walls against artillery fire.
In 1569, Matteo di Capua owned it, hosting poet Giovan Battista Marino. The Corsi family acquired it in 1607, followed by Giuseppe Andrea De Angelis in 1836, who heavily remodeled it, altering its medieval appearance.
The quadrangular castle sits atop a hill overlooking Caiazzo and the Volturno Valley. It has four towers: three round limestone ones and the square Torre di Lucrezia, named after Lucrezia d'Alagno. This tower includes multiple residential levels with vaulted ceilings and large windows, ending with a defensive rooftop.
The castle has two entrances, one near Torre di Lucrezia and another at the end of an old moat. The lower level retains its medieval service rooms with ogival arches, while a staircase leads to the 12th-century church of Santa Maria al Castello and the remodeled 19th-century residential quarters.
Nearby, remnants of Samnite polygonal walls from the 4th century BCE can be seen.
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.