In AD 757, al-Mansur sent a large army to
Cappadocia which fortified the city of
Malatya. In this same year, he confronted a group of the
Rawandiyya from the region of
Greater Khorasan that were performing
circumambulation around his palace as an act of worship. To consolidate his power al-Mansur founded the new imperial residence and palace city Madinat as-Salam (
the city of peace), which became the core of the Imperial capital
Baghdad. Al-Mansur laid the foundations of Baghdad near the old capital of
al-Mada'in, on the western bank of the
Tigris River, a location acceptable to him and his commanders. The circular city of about 2.4 km diameter was enclosed by a double-thick
defensive wall with four gates named Kufa, Syria, Khorasan, and Basra. In the center of the city al-Mansur erected the caliph's palace and the main
mosque. Al-Mansur had built Baghdad in response to a growing concern from the chief towns in
Iraq,
Basra, and
Kufa that there was lack of solidity within the regime after the death of Abu'l 'Abbas (later known as
al-Saffah). Another reason for the construction of the new capital was the growing need to house and provide stability for a rapidly developing Abbasid bureaucracy forged under the influence of
Iranian ideals. Al-Mansur pursued his vision of a powerful centralized caliphate in the new Muslim imperial capital of Baghdad. The city was populated with men and women of different faiths and cultures from all over the Islamic world. The Baghdad populace included
Christian,
Zoroastrian and
Jewish minorities and communicated in Arabic. Al-Mansur pursued Islamization by staffing his administration with Muslims of varied backgrounds. Baghdad became one of al-Mansur's lasting achievements. His rule was largely peaceful as he focused on internal reforms, agriculture and patronage of the sciences, In 764 al-Mansur's son
al-Mahdi was made the designated heir to the caliphate, taking precedence over al-Mansur's nephew
Isa ibn Musa, who had been named the designated successor when al-Mansur was crowned caliph. This change in succession was opposed by parts of the Abbasid family and some allies of Isa ibn Musa in
Khurasan, but was supported by the Abbasid army. Al-Mansur had cultivated support for his son's accession since 754, while undermining Isa ibn Musa's position within the Abbasid military.
Al-Tabari writes in his
History of Prophets and Kings: "Abu Ja'far had a mirror in which he could descry his enemy from his friend." Al-Mansur's
secret service extended to remote regions of his empire, and were cognizant of everything from social unrest to the price of figs, making Mansur very knowledgeable of his domains. He rose at dawn, worked until
evening prayer. He set the example for his son and heir. According to historic sources al-Mansur advised his son: “put not off the work of today until tomorrow and attend in person to the affairs of state. Sleep not, for thy father has not slept since he came to the caliphate. For when sleep fell upon his eyes, his spirit remained awake.” Notably frugal, al-Mansur was nicknamed Abu al-Duwaneek (“the Father of Small Change”), kept close tabs on his
tax collectors, and made sure
public spending was carefully monitored. He is reported as having said “he who has no money has no men, and he who has no men watches as his enemies grow great.” ==Islamic scholars under him==