where his rearguard was wiped out by Basque and Gascon rebels (this disaster inspired the epic Chanson de Roland). Charlemagne was also attacked by Sulayman's relatives, who had freed Sulayman. Now Abd al-Rahman could deal with Sulayman and the city of Zaragoza without having to fight a massive Christian army. In 779 Abd al-Rahman offered Husayn, one of Sulayman's allies, the job of Zaragoza's governorship. The temptation was too much for al-Husayn, who murdered his colleague Sulayman. As promised, al-Husayn was awarded Zaragoza with the expectation that he would always be a subordinate of Córdoba. However, within two years al-Husayn broke off relations with Abd al-Rahman and announced that Zaragoza would be an independent city-state. Once again Abd al-Rahman had to be concerned with developments in the Upper March. He was intent on keeping this important northern border city within the Umayyad fold. By 783 Abd al-Rahman's army advanced on Zaragoza. It appeared as though Abd al-Rahman wanted to make clear to this troublesome city that independence was out of the question. Included in the arsenal of Abd al-Rahman's army were thirty-six siege engines. Zaragoza's famous white granite defensive walls were breached under a torrent of ordnance from the Umayyad lines. Abd al-Rahman's warriors spilled into the city's streets, quickly thwarting al-Husayn's desires for independence. Legacy and death Social dynamics and construction works After the aforementioned period of conflict, Abd al-Rahman continued in his improvement of al-Andalus' infrastructure. He ensured roadways were begun, aqueducts were constructed or improved, and that a new mosque was well funded in his capital at Córdoba. Construction on what would in time become the world-famous Great Mosque of Córdoba was started circa the year 786. Abd al-Rahman knew that one of his sons would one day inherit the rule of al-Andalus, but that it was a land torn by strife. In order to successfully rule in such a situation, Abd al-Rahman needed to create a reliable civil service and organize a standing army. He felt that he could not always rely on the local populace in providing a loyal army; and therefore bought a massive standing army consisting mainly of Berbers from North Africa as well as slaves from other areas. The total number of soldiers under his command was nearly 40,000. As was common during the years of Islamic expansion from Arabia, religious tolerance was practiced. Abd al-Rahman continued to allow Jews and Christians