The white marble Arch of Septimius Severus at the northwest end of the Roman Forum is a triumphal arch dedicated in AD 203 to commemorate the Parthian victories of Emperor Septimius Severus. and his two sons, Caracalla and Geta.
After the death of Septimius Severus, his sons Caracalla and Geta were initially joint emperors. Caracalla had Geta assassinated in 212; Geta's memorials were destroyed and all images or mentions of him were removed from public buildings and monuments. Accordingly, Geta's image and inscriptions referring to him were removed from the arch.
The arch was raised on a travertine base originally approached by steps from the Forum's ancient level. The central archway, spanned by a richly coffered semicircular vault, has lateral openings to each side archway, a feature copied in many Early Modern triumphal arches. The Arch is about 23 metres in height, 25 metres in width and 11.85 metres deep.
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.