Kar Tukulti Ninurta (modern Tulul al Aqar) was built by Tukulti Ninurta I, just across the river and 3 km upstream from Assur.
A canal bisected Kar Tukulti Ninurta along the north-south axis, piercing even through the core walled royal-administrative quarter. At the southern end of the canal was a monumental gate; the north end stopped short of the opposite end of Kar Tukulti Ninurta. To the west of the canal were monumental complexes, including two palaces at the northwest edge of the city and another right on the river.
There was a ziggurat in the middle of the city's western half, attached to which was the Assur Temple. Tukulti Ninurta I celebrated his new capital with commemorative inscriptions on alabaster tablets found at Assur and Kar Tukulti Ninurta:
(46-66) At that time the god Aššur, my lord, requested of me a cult centre on the bank opposite my city, the desired object of the gods, and he commanded me to build his sanctuary. At the command of the god Aššur, the god who loves me I built before my city Aššur, a city for (the god) Aššur on the opposite bank, besides the Tigris, in uncultivated plains and meadows where there was neither house nor dwelling, where no ruin hills of rubble had accumulated, and no bricks had been laid. I called it K?r-Tukulti-Ninurta. I surrounded it with two walls, I heaped up heaps of earth in front of the wall and I dug a big moat following the circumference of the wall. In my city Kar-Tukulti-Ninurta which I love I constructed magnificent daises to serve as armchairs for the great gods and goddesses, my lords. I cut straight as a string through rocky terrain, massive and strong mountains. I cut a wide path for two watercourses of life which carry abundance for my city Kar-Tukulti-Ninurta. I transformed its plains into irrigated (fields). I arranged for regular offerings to Aššur and the great gods, my lords, in perpetuity from the produce (fish) of the waters of that canal.
Color plaster paintings decorated the palace: exteriorly, the north and south sides of the terrace; and interiorly, much of the palace walls. Dominant botanical motifs were rosettes, palmettes, lotus blossoms and the sacred tree. Color plaster was formed by mixing clay with sand and vegetable matter to form blue, red and black.
Kar Tukulti Ninurta was abandoned after the death of Tukulti Ninurta I, who was presumably assassinated by one of his sons.
The North Palace had an enormous terrace that has yielded fragmentary wall paintings. The terrace was 18m high, giving it the dominance of a ziggurat, and was accessed by a courtyard paved with unique rhomboid bricks and decorated with glazed green and yellow tiles. Texts found at Kar Tukulti Ninurta mention Hurrian families deported from Upper Mesopotamia to build Tukulti Ninurta I's building projects; the unique style of the Royal Palace likely arose via their influence.
In an innovative move, the ziggurat and temple complex were integrated. The cult room adjoins the ziggurat, and the cult nice is built into the ziggurat itself. Although the major deity was Assur, texts found at Kar Tukulti Ninurta indicate that his sanctuary was shared by many other deities of the Assyrian pantheon.