The Caltrops of Ginnoth are obstacles built to stop the advance of naval vessels. They consist of large objects of varying shapes and sizes, submerged in the waters of Ginnoth. The first use of the term "Caltrops of Ginnoth" was when the elderaunts of Selûn, then a city-state, sunk vessels in the channels as a way of deterring pirate raids from the Buccaneer Archipelago.
The lighthouses are lit to show the way into the safe channels of Ginnoth, but when under threat, they all go dark, and the Ora Tubruš begins moving them into defensive positions. Only the navy knows the safe lanes for any given time of the day.
The Caltrops of Ginnoth is one our greatest national defenses. They have led to the drowning of thousands over the centuries - mostly in times of war, but also in times of peace.
- Admiral Hurtugen, from his book on naval history of the Ivory Asylum - "The Caltrops of Ginnoth"
Caltrops of Ginnoth vary in size and shape, with some as large as a ship. These are practically immovable and were built in place. They serve as points for guiding ships into them and used in conjunction with smaller, movable caltrops. Some of the caltrops are designed to reflect sound - having built with concave shapes to make underwater sound waves reverberate back from them. These were built to be used against underwater attackers with the defenders dropping an explosive underwater and then have it detonate near one of these caltrops or between a group of them. They are not that effective given the conditions for them to come into use, yet they are one of many different shapes that a Catrop of Ginnoth can come in.
In the Third Epoch, Ivory Asylum grew to be a dominant naval power. The usefulness of the Caltrops of Ginnoth has declined with their rise in naval supremacy.