horreum

right|thumb|Reconstructed horreum at the Saalburg fort in Germany

A horreum (plural: horrea) was a type of public warehouse used during the ancient Roman period. Although the Latin term is often used to refer to granaries. By the end of the imperial period, the city of Rome had nearly 300 horrea to supply its demands. The biggest were enormous, even by modern standards; the Horrea Galbae contained 140 rooms on the ground floor alone, covering an area of some 225,000 square feet (21,000 m2). They provided storage for not only the annona publica (public grain supply) but also a great variety of resources like olive oil and foodstuffs. The amount of storage space available in the public horrea can be judged by the fact that when the emperor Septimius Severus died in 211 AD, he is said to have left the city's horrea stocked with enough food to supply Rome's million-strong population for seven years. Smaller (though similar) horrea were a standard feature of Roman towns, cities and forts throughout the empire; well-preserved examples of military horrea have been excavated on Hadrian's Wall in England, notably at the forts of Housesteads, Corbridge and South Shields.