I watched a documentary about the pyramids, and one of the pyramid was designed to keep water from coming into it, but the vents were angle downwards, so in case of a flood, the water will rise upward and pushes more air in the chambers but prevent the water from coming into the chambers of the pyramid. And in one of the books that they have found said this:
Now the multitude were very ready to follow the determination of Nimrod, and to esteem it a piece of cowardice to submit to God; and they built a tower, neither sparing any pains, nor being in any degree negligent about the work: and, by reason of the multitude of hands employed in it, it grew very high, sooner than any one could expect; but the thickness of it was so great, and it was so strongly built, that thereby its great height seemed, upon the view, to be less than it really was. It was built of burnt brick, cemented together with mortar, made of bitumen, that it might not be liable to admit water. http://en.wikipedia.org/wiki/Nimrod
And so they were trying to protect themselves from God's wrath and which that had offended God.
The Hebrews had branched from the Mesopotamian and
became wanderers that lived on the borders of the cities,
like roaming Gypsies, a nomadic tribe, a people without a nation.