Archaeological site Chellah in Rabat

You're standing at Chellah, on the south bank of the Bou Regreg river in Rabat. Start with the big gate in the wall. It's made of brick and cut stone, with a horseshoe arch, a frame of lobed arches around it and carved shells in the corners. Running around the edge is an Arabic inscription in angular Kufic script. It says the gate was finished in 1339, under Sultan Abu al-Hasan. Now look at the two towers beside it. They're eight-sided at the bottom and square at the top. Walk through and the passage takes a sharp turn. Very inconvenient for attackers.