Amr Iban El-As chose the plain close to the fortress of Babylon, to build the new arab capital in Egypt. Here he built his mosque which still stands though repeatedly altered or restored and here he began and foundation of the city which he called El Fustat which remained the capital of Egypt for more than three centuries, until El Kahira (Cairo) was founded close by 969. The new capital spread rapidly and soon became one of the chief cities of the Mohamedan Empire. The houses were at first of one storey but later they grew bigger and higher until some of them consisted of five stories.From El-Fustat, Abdul Aziz Ibn Merwan moved to Helwan (near Memphis, on the opposite bank of the Nile). Here, he planned the city, built houses, mansions and mosques, planted orchards and palm groves, and caused a Nilometer to be erected.