The Altar of Hieron is a monumental grand altar in the ancient quarter of Neapolis in Syracuse. It was built in the Hellenistic period by King Hiero II and is the largest altar known from antiquity.
The structure is aligned roughly north-north-west to south-east-east, and is located in the Neapolis. Almost nothing except the foundations of the structure survive today. The structure was partly built from masonry blocks and partially carved from the living bedrock. The altar itself is 20.85 metres wide and 196 metres long (exactly one Doric stade). This makes it the largest altar known from the ancient world.
The altar is mentioned by Diodorus Siculus, who attributes its construction to Hiero II. Stylistic analysis of the sculptural fragments from the altar confirms this, showing that they were made at the same time as the third phase of the nearby Greek theatre, which belongs after 235 BC. The votive deposit in the natural grotto under the eastern side of the altar shows that the area was already a sacred site in the Archaic period, not long after the city of Syracuse was established.
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.