Database: Great Chain

Built some time around 1000CE, the Great Chain was an ingenious - if slightly mad - defensive measure. Anchored to two large towers and strung across the mouth of the Golden Horn, the chain's primary purpose was to prevent enemy ships from sailing up the waterway and attacking the sensitive and poorly defended ports of Constantinople's interior.

As low tech as this sounds, the chain performed admirably on more than a few occasions for more than 400 years, and in 1453, it so vexed the Sultan Mehmet II that he was forced to improvise an even stranger plan to circumvent the Byzantine defenses: he pulled his warships over the hills of Galata and slid them on greased tracks into the Golden Horn, far upriver from the chain. It just goes to show that crazy is often the only way to beat crazy.