God commanded the ancient Israelites, through his servants (Moses, Aaron), regarding how to set up their wilderness camp in a particular way. The camp, set up right after the children of Israel left Egyptian slavery, would be organized by groups of tribes located on each of the camp's four sides (Numbers 2).
The tribal camps of Judah, Issachar and Zebulon were placed together on one side of the tabernacle (the eastern side) and were collectively under Judah's banner. The total number of fighting men they had was one hundred and eighty-six thousand four hundred - the largest of the four sets of tribes. Judah was also told how it was to march out of camp - it was to march out as the first division (verses 3, 9).
The tribal camps of Reuben, Simeon and Gad were placed together on another side of the tabernacle (the southern side) and were collectively under Reuben's banner. They had a total number of 151,450 fighting men and were told to march out of camp second, after Judah's division of about 186,000 (verses 10, 16).
The tribal camps of Ephraim, Manasseh and Benjamin were placed together on yet another side of the tabernacle (on the western side of the camp) and were collectively under Ephraim's banner. They had 108,100 men in their army and were required to march out of camp third (verses 18-24).
The tribal camps of Dan, Asher and Naphtali were placed together on the final side of the tabernacle (the very northern side of the camp) and were collectively under Dan's banner. The had a total of 157,600 men who could fight and were told to march last out of the camp (verses 25, 31).
Because God dedicated the tribe of Levi to serving as priests, they are not numbered among those who could fight. The Levites were required to march in the middle of Israel - with two divisions in front and two in back - as they carried then Tent of Metting (verses 17, 33).
According to the Bible, the total strength of Israel's wilderness army after they left Egypt was 603,550 men.