In the valley of the Roussenski Lom River, in north east Bulgaria, a complex of rock-hewn churches, chapels, monasteries and cells developed in the vicinity of the village of Ivanovo. The caves in the region had been inhabited by monks from the 1220s, when it was founded by the future Patriarch of Bulgaria Joachim I, to the 17th century, where they hewed cells, churches and chapels out of solid rock. At the peak of the monastery complex, the number of churches was about 40, while the other premises were around 300, most of which are not preserved today.
Second Bulgarian Empire rulers such as Ivan Alexander and Ivan Asen II frequently made donations to the complex, as evidenced by donor portraits in some of the churches. Other patrons included nobles from the capital Tarnovo and nearest big medieval town Cherven, with which the monastery complex had strong ties in the 13th and 14th century. It was a centre of hesychasm in the Bulgarian lands in the 14th century and continued to exist in the early centuries of the Ottoman rule of Bulgaria, but gradually decayed.
The monastery complex owes much of its fame to 13th- and 14th-century frescoes, preserved in five of the churches, which are thought of as wonderful examples of Bulgarian mediaeval art. The rock premises used by the monks include the St Archangel Michael Chapel ('The Buried Church'), the Baptistery, the Gospodev Dol Chapel, the St Theodore Church ('The Demolished Church') and the main Church, with the 14th-century murals in the latter one being arguably the most famous of all in Ivanovo and noted as some of the most representative examples of Palaeologan art.
Many century-old inscriptions have also been preserved in the monastical premises, including the famous indented inscription of the monk Ivo Gramatik from 1308–1309.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.