How according to the history Alexander ordered his army onward to the land of King Darius.

After staying awhile in Jerusalem Alexander mobilised his army and departed, making his way to the other cities of the land which all surrendered to him without the slightest resistance. And because of their friendly reception he graciously took them into his favour: from some, it might be said, he took a little and to others he gave as he saw fit.

It was at this point that some men who'd escaped from the city of Tyre took refuge at the court of King Darius, and told him how the great conqueror Alexander was advancing towards him and bringing every region in his path under his dominion: all were powerless to resist him. Darius was deeply angered by this news: he'd imagined that, since he'd earlier written to Alexander telling him to desist from such action, he'd been behaving accordingly. Having heard nothing of him for some time (the reason being that Alexander had had numerous distractions, as you've heard in the course of this story), Darius had assumed that Alexander had beaten a retreat. So he decided to send him new letters to find out what his intentions were; and this he did: he dictated letters immediately and gave them to his messengers along with a number of gifts, with strict orders not to stop until they'd delivered them to Alexander on his behalf and discovered exactly what kind of man he was, this King Alexander who was earning such a mighty reputation.