Megara Hyblaea is an ancient Greek colony in Sicily It was founded about 728 BC by colonists from Megara in Attica. In 628 the city established a colony at Selinus but in 483 was destroyed by the Syracusan leader Gelon. The city had a brief independent existence in the 4th century BC, when it issued coinage, but is heard of mainly as a fortified place.
Excavations carried on in 1891 led to the discovery of the northern portion of the western town wall, which in one section served at the same time as an embankment against floods. There is also an extensive necropolis, about 1500 tombs of which have been explored, and of a deposit of votive objects from a temple. The harbour lay to the north of the town.
In the mid-seventh century, the city was organised according to a regularised plan. An agora emerged with stoas on its north and eastern sides. This is one of the earliest known agoras.
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.