The ancient Greeks called armoured cavalry "Kataphraktos" (pl. "Kataphraktoi") which translated means roughly "covered, protected" or "armoured". The term was later borrowed by the Romans (the Latin variant in the Roman Empire being "Cataphractarii") and until the Middle Ages in Europe, continued to be used to designate armoured cavalry. However, as with other types of cavalry, heavy cavalry was not employed in any significant capacity in wars between the Greek city states until later, mainly due to the prevalence of hoplite warfare as well as the mountainous terrain of Central Greece. The lack of suitable grassland and excess grain supply necessary for the production of good cavalry mounts was also crippling to the establishment of an effective cavalry force, the noted Greek mercenary and writer Xenophon once saying that a horse farm was the most expensive type of establishment to keep running.