Sabbath Day's Journey

In the book of Numbers chapter 1 and following there's a breakdown of of ancient Israel where the tabernacle is supposed to be. The tribes that are the furthest away from the tabernacles as tradition holds is that they were no more than than 2,000 cubits or 3,000 feet which is about half between a half and three quarters of a mile. That became a Sabbath day's journey because that's how far they had to walk to get to thetabernacle to worship but it was an extra rabbinical rule that they just made up on their own.