https://en.wikipedia.org/wiki/Castra
In the Roman Republic and the Roman Empire, the Latin word castrum, plural castra, was a military-related term.. In Latin usage, the singular form castrum meant 'fort', while the plural form castra meant 'camp'. The singular and plural forms could refer in Latin to either a building or plot of land, used as a fortified military base.. In English usage, castrum commonly translates to …