Khalid ibn Walid was also known as Sayf Allah al-Masl¿l (Drawn Sword of God), a companion of the Prophet and noted for his military tactics and prowess. It was under his military leadership that Arabia, for the first time in history, was united under a single political entity, the Caliphate. His strategic achievements include the conquest of Arabia, Persian Mesopotamia and Roman Syria. He is also remembered for his decisive victories at Yamamah, Ullais and Firaz, and his tactical successes at Walaja and Yarmouk.