Derry's walls were originally built by the Irish Society between 1613 and 1619. They were built with the intention of protecting the Scottish and English planters that had moved to Ulster as part of the Plantation of Ulster that had been established by James I. It was a direct consequence of the previous settlement being destroyed by Irish chieftain Cahir O'Doherty during O'Doherty's rebellion. As a result of the building of the city's defences by the Irish Society, which was a consortium of livery companies based out of the City of London, the city was officially renamed Londonderry in the 1613 royal charter. This is what has subsequently led to the naming dispute for the city and county of Derry/Londonderry.
The walls are at the centre of the historic city of Derry and within them are a number of Derry's most important landmarks including the Apprentice Boy's Hall and St. Columb's Cathedral.
The walls are about 1 mile in circumference and contain many of the city's most important landmarks. The entire length of the walls is fully accessible on foot. There are seven gates in total, four of which were built at the same time as the walls themselves and three were added later.
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.