After the brilliant victory at Gaugamela, the next stage would be a walk for Alexander. Perhaps he had not yet intuited when he approached the immense brick walls of Babylon. Herodotus, who had visited it a century before, affirms that the walls surrounded one hundred and fifty-five square kilometers, in which it was possible to obtain crops during a siege. Even the old fortifications of Nebuchadnezzar, which at that time formed the inner circle, were immense. The outer walls were fifty-five meters thick and one hundred and twenty high. Cyrus had taken the city without a fight, but Alexander must know the more realistic version of Xenophon. The mass of Babylon was visible miles before, on the other side of the plain, which augured a siege at least as colossal as that of Tire. He did not even need to make an acknowledgment. On the way, Alexander met Mazaeus, satrap of Babylon, who offered him the unconditional surrender of the city. It had been a little more than a century since Babylon had made her last attempt to break free from Persia and Xerxes had crushed her severely. Its population lover of the luxury was desafecta or indifferent, the members of the garrison were disappointed with the Persian king. When he was offered that surprising gift, as was to be expected, Alexander suspected that it was a trap and continued to advance in battle order, at the head of the vanguard. However, the walls were defenseless, the hundred doors wide open and the drawbridges lowered. He entered as king of Babylon, on October 22, in a gold-plated car, amid splendors that the victories of the Caesars never surpassed. The main thoroughfare of the city was dotted with flowers and perfumed with incense. They led the procession rare and exotic gifts, select steeds and carts that carried caged lions and leopards; attended by magicians and priests, the real singers of praises sang hymns and the cavalry of Mazaeus paraded. As always with Alexander, there was an absence of a Roman ornament: the spectacle of the captives humiliated and chained.
Thus a triumphal entry was made in his new capital, with a shower of flowers, and an atmosphere charged with the intense aroma of the altars placed on both sides of the parade, without even the slightest attempt at resistance. Alexander thus took possession of the Palace and the Treasury, made a formal sacrifice in the gods of the city, Bel-Marduk, in his famous ziggurat, following the protocol prescribed by the local priesthood. The order to restore the zigú, very spoiled by the troops of Xerxes, for the order of the year 331 b. C., in preparation for a colossal reconstruction that his premature death truncated.