A Casemate is a heavy duty structure originally a valuted chamber in a fortress. Today the military use the term for a fortified gun emplacment. In civilian use a casemate may be a tunnel cut into a rock face with armoured doors, used for storing volatile goods. Fortifications (Latin fortis, strong, and facere, to make) are military constructions designed for defensive warfare. ... Alternative meanings: vehicle armour, Armor (novel) A hoplite wearing a helmet, a breastplate and greaves (and nothing else). ...
A large part of a decorated platter was found in the bottom of the casemate, along with pieces of broken glass from a fine set of tableware.
The find is a casemate - in the word's original sense of a vaulted chamber in a fortress.
The space is created by the supports for the outside wall, which at the same time is holding up a 40 centimeter (15.7 inch) thick layer of timber that served as the floor for a cannon site.