Nehemiah obviously had a standard of height in mind for the wall his men were to build. Instead of reaching all the way for the top in their own section, the workers worked in such conjunction with their adjacent labourers that the wall went up uniformly. That the wall is presently up at half its intended height means that enemies no longer have an open piece of wall through which they might easily infiltrate the city.
6 So we built the wall. And all the wall was joined together to half its height, for the people had a mind to work.