The Diamanteau is a type of heavy, multi-decked vessel used exclusively by governments for oceanic trade. It was designed by Lasant to protect the diamond trade coming from its main Bocan port of Avirre Tove, based off of the Arcish Galeón design. Diamanteaux combine the large cargo hold of the Trade Galeón with the defensive configuration and added cannon space of the War Galeón, and adds an armor-plated hull and magically treated sails for even greater combat prowess.
When the Arcish Treasure Fleet was captured in 449, it began using diamanteaux for its own treasure fleet. The cost of even one diamanteau is so high that it is almost a treasure itself, and only governments would normally be seen using them. To attack a treasure fleet based around diamanteaux would require a well-armed, well-trained armada.