The Viking Ship Museum (Vikingeskibsmuseet) is the Danish national museum for ships, seafaring and boatbuilding in the prehistoric and medieval period.
Around the year 1070, five Viking ships were deliberately sunk at Skuldelev in Roskilde Fjord in order to block the most important fairway and to protect Roskilde from enemy attack from the sea. These ships, later known as the Skuldelev ships, were excavated in 1962. They turned out to be five different types of ships ranging from cargo ships to ships of war.
The Viking Ship Museum overlooks Roskilde Fjord and was built in 1969 especially to exhibit the five newly-discovered ships. In the late 1990s excavations for an expansion of the museum uncovered a further 9 ships including the longest Viking warship ever discovered, at 36 metres.
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.