Bobastro is the ruins of an old castle in the Province of Málaga. The castle was of Roman origin, but rebuilt by Umar ibn Hafsun during his rebellion against the Caliphate of Cordoba in the 9th century.
There had been a structure at the site since Roman times. In 880 AD, Umar ibn Hafsun settled in the ruins of the old castle of Bobastro near Ardales, in which he incited the muwallads and mozarabs to join his cause against the unfair, heavy taxation and humiliating treatment they were receiving at the hands of Abd ar-Rahman II and his successors. The rebels constructed a church within the castle which lasted until the end of their autonomy on January 19, 928.
In 888 AD, Al-Mundhir of Córdoba was murdered at Bobastro by his brother Abdullah ibn Muhammad al-Umawi, who later succeeded him.
The Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.