The Basilica of Saints John and Paul on the Caelian Hill was built in 398 AD over the home of two Roman soldiers, John and Paul, martyred under the emperor Julian in 362. The church was thus called the Titulus Pammachii and is recorded as such in the acts of the synod held by Pope Symmachus in 499.
The church was damaged during the sack by Alaric I (410) and because of an earthquake (442), restored by Pope Paschal I (824), sacked again by the Normans (1084), and again restored, with the addition of a monastery and a bell tower.
The church has three naves, with pillars joined to the original columns. The altar is built over a bath, which holds the remains of the two martyrs. The apse is frescoed with Christ in Glory (1588) by Cristoforo Roncalli. Below this fresco are three paintings: a Martyrdom of St John, a Martyrdom of St Paul, and the Conversion of Terenziano (1726) by Giovanni Domenico Piastrini, Giacomo Triga, and Pietro Andrea Barbieri.
During excavations performed in the 19th century, a series of Ancient Roman rooms were discovered under the nave of the church. Some of these rooms date back to the first and fourth centuries AD. In one room an elegant third-century AD fresco depicting Proserpine and other divinities among cherubs in a boat can be found, as can traces of another marine fresco and mosaics in the window arches.References:
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.