'Fifties' in the Bible

your wives, your infants, and your substance, abide in the land which Moses hath given to you beyond the Jordan, and ye -- ye pass over by fifties, before your brethren, all the mighty ones of valour, and have helped them,

and the sons of Reuben, and the sons of Gad, and the half of the tribe of Manasseh, pass over, by fifties, before the sons of Israel, as Moses had spoken unto them;