A propylaea means an monumental gateway in ancient Greek architecture. Entrance into the Acropolis was controlled by the Propylaea. Though it was not built as a fortified structure, it was important that people not ritually clean be denied access to the sanctuary. It was one of several public works commissioned by the Athenian leader Pericles in order to rebuild the Acropolis hill at the conclusion of the Persian Wars. Pericles appointed his friend Phidias as the supervisor and lead architect of this massive project, which Pericles allegedly financed with funds appropriated from the treasury of the Delian League. According to Plutarch, the Propylaea was designed by the architect Mnesicles, about whom nothing else is known. Construction began in 437 BC and was terminated in 432, when the building was still unfinished.
The Propylaea survived intact through the Greek, Roman and Byzantine periods. During the period of the Duchy of Athens, it served as the palace of the Acciaioli family, who ruled the duchy from 1388 to 1458. It was severely damaged by an explosion of a powder magazine in 1656, foreshadowing the even more grievous damage to the Parthenon from a similar cause in 1687. A Frankish tower, erected on the south wing, was pulled down in 1874.
The core is the central building, which presents a standard six-columned Doric façade both on the West to those entering the Acropolis and on the east to those departing. The columns echo the proportions of the columns of the Parthenon.
The Greek Revival Brandenburg Gate of Berlin and the Propylaea in Munich both evoke the central portion of the Athens propylaea.
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.