The Latin word castra, with its singular castrum, was used by the ancient Romans to mean buildings or plots of land reserved to or constructed for use as a military defensive position. The word appears in both Oscan and Umbrian (dialects of Italic) as well as in Latin. It may have descended from Indo-European to Italic. In classical Latin the word castra always means "great legionary encampment", both "marching", "temporary" ones and the "fortified permanent" ones, while the diminutive form castellum was used for the smaller forts, which were usually, but not always, occupied by the auxiliary units and used as logistic bases for the legions, as explained by Vegetius. A generic term is praesidium ("guard post or garrison"). The terms stratopedon ("army camp") and phrourion ("fort") were used by Greek language authors, in order to designate the Roman castra and the Roman castellum respectively. In English, the terms "Roman fortress", "Roman fort" and "Roman camp" are commonly used for the castra. However the scholars' convention always requires the use of the word "camp", "marching camp" and "fortress" as a translation of castra and the use of the word "fort" as a translation of castellum and this type of convention is usually followed and found in all the scholarly works.

Gilles de Montmorency-Laval (1404–1440), Baron de Rais, was a Breton knight, a leader in the French army and a companion-in-arms of Joan of Arc. He is best known as a prolific serial killer of children.

A member of the House of Montmorency-Laval, Gilles de Rais grew up under the tutelage of his maternal grandfather and increased his fortune by marriage. Following the War of the Breton Succession, he earned the favour of the Duke and was admitted to the French court. From 1427 to 1435, Gilles served as a commander in the Royal Army, and fought alongside Joan of Arc against the English and their Burgundian allies during the Hundred Years' War, for which he was appointed Marshal of France.

In 1434/5, he retired from military life, depleted his wealth by staging an extravagant theatrical spectacle of his own composition and dabbled in the occult. After 1432 Gilles engaged in a series of child murders, his victims possibly numbering in the hundreds. The killings came to an end in 1440 when a violent dispute with a clergyman led to an ecclesiastical investigation which brought Gilles' crimes to light. At his trial the parents of missing children in the surrounding area and Gilles' own confederates in crime testified against him. Gilles was condemned to death and hanged at Nantes on 26 October 1440.