The Great Saint Martin Church (Groß Sankt Martin) foundations (circa 960 AD) rest on remnants of a Roman chapel, built on what was then an island in the Rhine. The church was later transformed into a Benedictine monastery.
In 1150, a fire destroyed much of Cologne and it is supposed that the entire church was destroyed. The Archbishop of Cologne Philipp I. von Heinsberg sanctified the new building in 1172, and the first phase of construction, the tri-apsidal structure was built, with three round apses meeting in the shape of a cross. This is the only element of the church still present today. The eastern end of the nave was completed before a further fire in 1185, as well as aisles on the Southside. At the northern apse, two Benedictine chapels were later added, built over the ruins of the previous abbey buildings.
In the middle of the 13th century, new walls for the three apses were completed, with larger windows. These provided a sought-after lightness to the interior. The nave was also made five meters longer, and the atrium in the west was built.
After the completion of the church in the 13th century, few modifications to the form of the church were undertaken. Most significant during this period were the various renovations needed for the four surrounding towers.
Reforms under abbots Jakob von Wachendorp (1439–1454) and Adam Meyer (1454–1499) provided a stronger financial footing for the Benedictine abbey. From this the inner decoration of the church was embellished, including figures from the altar, installed in 1509, that are still present today.
In 1707, the decaying interior walls were repaired and refurbished. Heinrich Obladen, then the abbot of Great Saint Martin, also purchased a new, larger organ for the church. New adornments for the Church took on a Baroque style, including golden bands for the pillars, dome and walls.
The church was badly damaged in World War II; restoration work was completed in 1985.
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.