Archaic term for a person who guards or watches over something. In modern Japanese, 守護者 or ガードマン are more common.
古い物語では、城の守り人が夜通し見張りをしていた。
In old tales, the castle guard kept watch all night.
Compound of 守り (mamori, 'protection') + 人 (hito, 'person'), with rendaku voicing of ひと to びと. The exact historical period of coinage is uncertain, but it follows a classical pattern for agentive nouns.