Why it looks like this

Caliph al-Mansur founded Baghdad in 762 as a planned circular city about two kilometres across, with four gates and the palace at the exact centre. It became the largest city in the world — but the Round City itself vanished centuries ago.

The Baghdad on this map grew along both banks of the Tigris instead: Rusafa on the east, Karkh on the west, joined by a chain of bridges. Straight avenues like Rashid Street were cut through the old lanes in the 20th century.