The Gozo Citadel, similarly to Mdina and what was known as the Castrum Maris in Malta, was designed to withstand a siege and this meant having food within the fortifications. During a siege, the population locked within has to rely on what is available on the inside. This system was similarly employed when Valletta was founded in the second half of the 16th century. Bread was the staple foodstuff, and refurbishments in the beginning of the 17th century saw the creation of these three large grain silos.

The silos have been recently restored and can now be visited. The grain silos are shaped like flasks and have a combined capacity of around 100 cubic metres. The largest of the three is almost 11 metres deep and measures around 3.6 meters at the widest part. After 1800 the silos seem to have fallen into disuse and were converted into water tanks as part of a plan to better supply the growing population of the capital with clean water. An impermeable layer of lime-based sealant was applied throughout to keep the water within the porous rock. The grain silos remained in use as water tanks until March 2004.