<P> Of the fortifications we know much more . In the north wall of Nimroud fifty - eight towers have been traced, and at Kouyunjik there are large remains of three walls, the lower part being of stone, and the upper of sun - dried bricks . At Khorsabad there are the remains of a wall, still 40 feet (12 m) high, built of blocks of stone 3 to 4 feet (1.2 m) thick, and the evidences wanting as to finishing of these is completely supplied by the sculptures, which show an extraordinary resemblance to medieval works of the same class . Tier upon tier of walls are represented, enclosing a great tower or keep in the centre . The entrances are great arched gateways flanked by square towers . These and the other towers have overhanging parapets just like the mediaeval machicolations, and are finished at top with battlements, remains of which have been found at Nimrud and Kouyunjik, and at Assur, the capital of Assyria before Nineveh . </P> <P> Of temples distinct from the palace we have a few supposed remains, but little is absolutely known as to their general form . </P> <P> But in Chaldea there are some enormous masses of ruins, evidently remains of the vast mounds which formed the substructure of their temples . The grandest of all these and the most interesting is the temple of Nabû at Borsippa (now Birs Nimrod), near Babylon, which has been identified as the temple of the Seven Spheres . This was reconstructed by Nebuchadnezzar, as appears by a well - known inscription . Another example is at Mugheir, which was 198 feet (60 m) by 133 feet (41 m) at the base, and is even now 70 feet (21 m) high, and it is clear that both it and the Birs were built with diminishing stages, presenting a series of grand platforms, decreasing in length as they ascended, and leaving a comparatively small one at top for the temple cell . This has been found, it is supposed, at the Birs Nimroud, of vitrified brick made in ancient ovens . </P> <P> Text sources indicate open space planning was a part of the city from the earliest times . The description of Uruk in the Epic of Gilgamesh tells of one third of that city set aside for orchards . Similar planned open space is found at the one fifth enclosure of Nippur . Another important landscape element was the vacant lot (Akkadian: kišubbû). </P>

How did the sumerian government change over time