fifteen kilometres (10 mi) from babylon was heliopolis. the muslim army reached heliopolis in july 640. it was the city of the sun temple of the pharaohs and was famous for its grandiose monuments and learning institutions. there was the danger that forces from heliopolis could attack the muslims from the flank while they were engaged with the roman army at babylon. with some detachments, 'amr and zubair marched to heliopolis. there was a cavalry clash near the current neighbourhood of abbaseya. the engagement was not decisive, although it resulted in the occupation of the fortress located between the current neighborhoods of abdyn and azbakeya. the defeated byzantine soldiers retreated to either the babylon fortress or the fortress of nikiû (now zawyat razin). at an unguarded point of the wall of heliopolis, zubair and some of his picked soldiers scaled the wall of the city, and after overpowering the guards, opened the gates for the main muslim army to enter the city. heliopolis was thus captured by the muslims. 'amr and zubair returned to babylo.