The Rotterdam painting is about half the size of the Vienna one. In broad terms they have exactly the same composition, but at a detailed level everything is different, whether in the architecture of the tower or in the sky and the landscape around the tower. The Vienna version has a group in the foreground, with the main figure presumably Nimrod, who was believed to have ordered the construction of the tower, although the Bible does not actually say this. In Vienna the tower rises at the edge of a large city, but the Rotterdam tower is in open countryside.