March to Iraq. In March 633 C.E. when Khalid bin Walid was quartered with his army at Yamama, he received orders from Abu Bakr that he should march to Iraq and start operations in the region of Uballa where the two rivers, the Tigris and the Euphrates, met. Four other columns each under the command of Muthanna, Mazar, Harmala, and Salma were also directed to proceed to Iraq to reinforce the main Muslim army under the command of Khalid bin Walid.
Hormuz. Uballa was the main port of Iraq and was the headquarter of the district then known as 'Dasht Meisan'. Uballa being a junction of many land routes was the gateway of Iraq and commanded great strategical importance. The Governor of the district was Hormuz, a veteran General and a skilful administrator. In the Persian administrative hierarchy, he held 'one hundred thousand dirham' rank, and was entitled to wear a gem studded cap worth one hundred thousand dirhams. He was an imperialist, very haughty and arrogant. He held the Arabs in contempt. His harshness and high handedness became the subject of a saying among the local Arabs "More hateful than Hormuz".
Khalid's letter to Hormuz. As soon as Khalid received orders to march to Iraq, he addressed a letter to Hormuz calling upon him to accept Islam. The letter read: "Submit to Islam and be safe. In the alternative you may agree to the payment of 'Jizya', and you and your people will be under our protection. Otherwise you will have only yourself to blame for the consequences for I bring a people who desire death as ardently as you desire life."
Preparations of Hormuz. Hormuz mustered his forces and set out from Uballa to meet the Muslim forces. On the direct route from Uballa to Yamama the first stage was Kazima, and Hormuz decided to give a battle to the Muslims at that place. His idea was that the Muslim forces should be kept away from Uballa. On arrival at Kazima, Hormuz deployed his army with a center and two wings, the right and the left. His men were linked together with chains, and in this state of affairs the Persians awaited the arrival of the Muslim forces.
Tactics of Khalid. Khalid gave a slip to the Persians, and instead of following the direct route to Uballa via Kazima, he followed the indirect route via Hufeir. Hufeir was much closer to Uballa than Kazima, and when Hormuz came to know that Khalid had already reached Hufeir, he was very much upset. He immediately ordered his forces to march to Hufeir. It was a weary two days march for the Persian forces, but when they reached Hufeir they found that the Muslim forces had left for Kazima. The Persians had no option but to march back to Kazima.
By the time the Persian forces reached Kazima, they were thoroughly exhausted. Khalid allowed them no time to rest. As the Muslim forces were already deployed for battle, the Persians were forced to go into action. The Persian forces were linked in chains, and it was the use of these chains, which gave the battle of Kazima, the name of the "Battle of Chains."
Duel between Khalid and Hormuz. The battle started with a duel between the army commanders. Hormuz ,Commander of the Persian forces, stepped forward and invited Khalid, Commander of the Muslim forces, to a duel. Hormuz instructed some of his men to remain close to him, so that when he gave a signal they should fall on Khalid and kill him. Hormuz and Khalid began to fight with swords and shields. Both the Generals were expert swordsmen, and the fight with swords proved to be a drawn battle. Thereupon, Hormuz suggested that they should drop the swords and wrestle. When the wrestling match was in full force, Hormuz gave the signal to his men to step forward and kill Khalid. Khalid realized the gravity of the situation. He was without sword and shield, and was obviously at the mercy of the Persian soldiers. Khalid, however, did not lose nerve. He held Hormuz fait in his grip, for as long as he held Hormuz in his grasp the other Persian soldiers could not harm him. In the Muslim ranks, a warrior Qa'qa'a bin Amr saw through the Persian game and decided to take immediate action. He spurred his horse and rushed to the spot where Khalid and Hormuz were wrestling. Before the Persians could realize, Qa'qa'a had killed all the Persians who had treacherously conspired to kill Khalid. Having been freed from the threat of the Persian soldiers, Khalid tightened his grip on Hormuz. Within a few moments, Hormuz lay motionless on the ground. Khalid picked up his sword, and drove it into the body of Hormuz.
Battle of the Chains. After having killed Hormuz, Khalid ordered an immediate attack on the Persian forces. The death of Hormuz had demoralized the Persians, but nevertheless, they fought hard. The Muslims assailed vehemently, but the chain-linked Persian infantry withstood all attacks. The Muslims redoubled their attacks, and the Persians were forced to fall back. The Persians found their chains to be a death trap, and as they retreated held together in chains they were slaughtered in thousands. Before night set in, the Muslims had won the battle.
Consequences of the battle of Kazima. In the battle of Kazima, which was the first confrontation between the Muslims and the Persians, the Persians so proud of their power met a humiliating defeat. Thousands of Persians were killed, and thousands of them were taken captive. The war booty that fell into the hands of the Muslims comprised wagons, armor, stores, costly garments, horses and a good amount of money. Four-fifth of the booty was distributed among the Muslim soldiers and one-fifth was sent to the Caliph at Madina. So large was the booty that the share of each cavalryman came to a thousand dirhams. The booty included the one hundred-thousand dirham cap of Hormuz studded with diamonds and pearls. The Caliph offered this cap as a present to Khalid. The battle of the Chains at Kazima unchained for the Muslims the gate of Iraq. The so-called uncivilized Arabs had defeated the Persians so proud of their civilization extending over a thousand years.