sanctuary (n.)
early 14c., "building set apart for holy worship," from Anglo-French sentuarie, Old French saintuaire "sacred relic, holy thing; reliquary, sanctuary," from Late Latin sanctuarium "a sacred place, shrine" (especially the Hebrew Holy of Holies; see sanctum), also "a private room," from Latin sanctus "holy" (see saint (n.)).

Since the time of Constantine and by medieval Church law, fugitives or debtors enjoyed immunity from arrest in certain churches, hence transferred sense of "immunity from punishment" (late 14c.). Exceptions were made in England in cases of treason and sacrilege. General (non-ecclesiastical) sense of "place of refuge or protection" is attested from 1560s; as "land set aside for wild plants or animals to breed and live" it is recorded from 1879.