At this point, under Charlemagne (747 / 48−814), a semicircular building with a diameter of about 89 meters was built, which gave the Ingelheim Palatinate its characteristic floor plan. Its curved shape was deliberately based on the architecture of antiquity. In front of the semicircular building was a large colonnade in the direction of the inner courtyard, reminiscent of a Roman villa. The semicircular building was entered from the outside through an imposing gate, which was located at its apex. It is known today under the name "Heidesheimer Tor" and was one of the main entrances to the Palatinate.
Two side gates that flanked the gate were made visible again through the excavations and renovation measures. they guided in the outer towers, the remains of which have also been uncovered today. At the left gate you can still see an original sandstone fall from the Carolingian construction period.
Under the Hohenstaufen rulers in the High Middle Ages, the outer round towers were torn down and the gate opening walled up. The gate was replaced by a defensive wall.
This reconstruction contributed to a castle-like fortification of the complex, which served to secure and enforce the Hohenstaufen territorial policy.