Roman Forum of Zadar is the largest on the eastern side of the Adriatic sea, founded by the first Roman Emperor Augustus, as shown by two stone inscriptions about its completion dating from the 3rd century.
Ancient Zadar (or Iadera as the Romans would say) was a Roman colony from 48BC until the disintegration of the Roman empire in the 5th century. After a violent earthquake in the 6th century, the buildings surrounding the forum were destroyed. The still standing elements and stones (then used to rebuild) were retrieved for various buildings.
Most striking is the decorative column marking the western side of the forum. Notice the chains still visible on the column. During the Middle Ages it was the 'pillar of shame' used to punish evildoers.
Continuing on the western side of the Forum, you come to the remains of the Capitolium which was an important temple consecrated to Jupiter, Juno and Minerva.
To round out an appreciation of Roman Zadar, take a look at Zadar's Archaeological Museum which displays artifacts from the Roman period as well as a scale model of the original Roman forum.
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.