The Imperial Palace in Ingelheim was erected in the second half of the 8th century. Charlemagne chose Ingelheim in 787 as the location for his winter quarters, arriving there before Christmas and remaining there without interruption until the middle of 788. However the palace was not completed before completed before 814. It served Emperors and Kings as a residence and place for governance until the 11th century. From the buildings of the Imperial Palace impressive relics above ground are preserved today. The greater part of the complex remains as foundation under ground level and allows it to be the basis for archaeological excavations to reconstruct the entire system of buildings.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.