A Man-at-arms was a type of soldier of the High Medieval to Renaissance periods. He was almost always a professional warrior in the sense of being well-trained in the use of arms, who served as a fully armoured heavy cavalryman. A man-at-arms could be a knight or nobleman, a member of a knight or nobleman's retinue or a mercenary in a company under a mercenary captain. Such men could serve for pay or through a feudal obligation. The terms knight and man-at-arms are often used interchangeably, but while all knights equipped for war certainly were men-at-arms, not all men-at-arms were knights.