The old St. Peter's Church was first mentioned in the 12th century, but the construction of the present Gothic church began in the 14th century. During the Reformation, the church became Protestant in 1529, but when Louis XIV conquered the city in 1683, parts of the church were returned to the Catholics and a wall was built to separate the two areas. Today, the part of the church on the side of the 22-November street is dedicated to Catholic worship while the part overlooking the Grand'rue is dedicated to Protestant worship.
The territory of present-day Germany was the epicentre of the face-off between Catholics and Protestants from the 16th century onwards. This led not only to a division of the region but also to divisions within the towns themselves, in which the churches regularly changed denominations. The “Simultaneum”, a form of religious tolerance that allowed Protestants and Catholics to share a church, became attractive to the leaders of these territories where consensus seemed impossible. The "Simultankirchen" (shared churches) are the descendants of this period, and of the unrest that followed; they constitute a unique heritage in Germany.
The church of St. Martin was probably founded around 1100 as a Romanesque church and replaced by a Gothic one between 1320 and 1370. At the time of the Reformation, the Simultaneum (a policy allowing public worship by the followers of two or more religious groups in the same church: Simultankirche) was established for St. Martin's Church, and both Protestants and Catholics have shared the church since 13 August 1548. This was especially true for the nave and the choir which remained purely Roman Catholic. This condition was established by the Peace of Westphalia and still exists today. According to the land register, the owner of the parish church is the Gemeinschaftliche Kirchenpflege Biberach.
Altenberg Cathedral was founded in the 13th century as an abbey church by the Cistercians. The church, including its interior, is strictly Gothic in style. During secularization (1803) the abbey was dissolved, and parts of the abbey later became a chemical factory. An explosion largely destroyed the abbey buildings in 1815. After the ruins of the church were donated to the Prussian state, Frederick William III (1797 -1840) gave substantial support for the restoration of the abbey church on the condition that it be used as a common church. The first Protestant service took place on 13 August 1857. Further phases of restoration took place from 1894 to 1912 and in the 1960s.
The Abbey Church of Otterberg was founded in 1143 by Cistercians as the abbey church of a daughter abbey of the Eberbach monastery. In the 15th century, the monastery slowly declined. In 1504, and in 1525 during the Peasants' War, the monastery was burned and plundered. At the end of the 16th century, the abbey church began to be used simultaneously by the Catholic and Protestant parishes, but not without causing disputes. In 1708, therefore, a separation wall was built between the two spaces. The choir hall with the transept is now used as the Catholic part, and the remaining nave as the Protestant part. In 1979, the wall was removed as part of a major renovation, but the structure of the property was not changed.
The Church of St. Juliana is said to have been founded in 736 by St. Pirmin as part of a Benedictine monastery. The oldest document in which the church is mentioned dates from 1277, but from 1370 the collegiate church was rebuilt in several phases. The Reformation was officially introduced into the church in 1556. During the Peace of Rijswijk, which succeeded the War of the Palatinate Succession in 1697, religious practice in the church was granted to Catholics. However, as conflicts between denominations continued to occur, the Elector began in 1705 to separate all the shared churches by a wall. Gone from most of the shared churches, the wall still exists in the church of Sainte-Julienne. In 2007, on the 300th anniversary of the separation, Protestant and Catholic parishes agreed to open the separation wall. The wall was pierced and gates and a few steps were built, which now connect the Protestant and Catholic sides.
Wetzlar Cathedral, which is not the seat of a bishop, was built from the 13th to the 15th century on a Romanesque church, but its construction remained unfinished. As the number of canons and vicars of the church declined throughout the 16th century, an agreement was reached in 1561 for the joint use of the church by the Catholic canons and the increasingly Lutheran inhabitants of Wetzlar. In the following years, however, there were repeated disputes: the canons prohibited Lutherans from entering the church. In return, the Protestant community occupied the nave in 1567. From 1571, the canons no longer celebrated mass in the choir of St. Mary's Church. Nevertheless, the church choir remained a Catholic institution upon the intervention of the Archbishop of Trier. At the end of the 16th century an agreement was finally reached.