We were beginning to see what two years of Memnon had done to us. We had a team.

Three days of careful movement, advancing from one strong-point to the next, the two groups on either ridge supporting each other, and we were through. The plains around Tarsus were so green they seemed to burngreen, and I could see the sea in the distance. Behind me, the army began to shout, ‘Thalassa!’ like Xenophon’s hoplites, and men hugged each other.

Arsames was burning the plains, scorching the crops to deny us food.

We picked up a bunch of angry peasants who claimed he was going to burn the city.

Parmenio was commanding the advance guard himself, and he told us to go for it. His assumption was that if the local people viewed us as liberators, the worst we’d get was a bloody nose.

Alexander was in the rear. Rumour was that he’d drunk too much the night before with Parmenio, and could barely ride.

Kineas’s Athenians were the first into Tarsus, because he went by road while I covered his flanks and two heavy troops of Thessalians covered mine. We found Arsames just north of the city and had a sharp skirmish, but he had no confidence, or he was a traitor, or whatever happened inside that kind of man’s head, and his troops ran. Kineas secured the north gate – more, he said later, by happenstance than by plan.

We took Tarsus intact, granaries and all. And Arsames rode off to the east to join King Darius, whom he had just betrayed, either by crass incompetence or by greed.

Alexander was one of the last men into the city. He’d spent the day, unaware we were fighting, driving the stragglers across the last of the desert and up into the Gates, making sure that no one lay down and died. It was noble of him, but when he came in through the north gate, he was tired, hot and surly, because we’d fought a nice little action, taken prisoners, seized a town, and all without him.

And we were through the greatest obstacle in Asia.

But he brightened up when he heard the tale, and he gave Kineas his hand and thanked him. Kineas adored the king. He didn’t see the flaws beneath the surface. To Kineas, Alexander wasthe hegemon of the League, leading us to revenge against Persia. And the hegemon’s thanks made him glow with joy.

Alexander rode along with Philotas, Kineas and Parmenio. I trailed behind. He rode down to the river, which flowed icy cold from the mountains we’d just traversed.

Kineas put his hand on the king’s bridle when Alexander moved to dismount. ‘I lost a horse to that river this morning, lord,’ Kineas said.

Parmenio laughed. ‘Don’t be such a nursemaid, Athenian! In Macedon, we swim in ice.’

The king stripped off his chiton and boots and dived into the clear water and surfaced, spluttering. Hephaestion leaped in after him, shrieked and swam back to the bank.

He crawled out, laughing. ‘Zeus! My balls are gone.’

We all joined him. I was stripping off my own chiton when I realised that the king wasn’t there. Everyone else realised it at the same time, and we charged into the water – me, Philotas, Seleucus, Black Cleitus, Philip the Red and Kineas. We found him floating just under the surface, and we hauled him to the bank. He was having some sort of fit, and his skin was dead white. He’d taken in some water, too.

Everyone assumed he’d breathed too much water, and we did what men do for a drowning victim – a blanket, and Hephaestion forced air into his lungs, and he breathed.

But an hour later, he was no better.

By nightfall, he was speechless and his eyes were closed and his breathing was rough.

Parmenio took command. Thaïs had agents here, and they reported that Darius was just ten or fifteen days to the east. We were too close to break off in safety. Parmenio held a command council the first night of the king’s illness and told us that, while he doubted the wisdom of facing the Great King, he was going to accept battle if he could get it on his own terms.

Perhaps I defame him, but I heard a man making his bid for the kingship. If he defeated Darius, no Macedonian would stand in his way. I think we all knew it.

After the meeting, I went to the king’s tent. The vultures were gone. I wondered if they were already clamouring for Parmenio’s attention.

I gave the password to the guards and entered the tent. Alexander was awake. He was pale in the lamplight, and only his head showed. His eyes were wild, and his hair was plastered to his forehead.

I sat down, and Hephaestion got up with an ill grace and made room for me.

‘I must get up,’ Alexander said.

I shook my head. ‘Parmenio is no fool. He’ll fight.’

But Alexander shook his head, and his whole body shook. ‘This is the battle!’ he said, with so much force that they must have heard him in the streets of Tarsus. ‘This is the battle. Not for Parmenio! For me!’ He all but writhed.

‘He just keeps saying that,’ Hephaestion complained. ‘I can’t get him to sleep.’

I took his hands. ‘There will be other fights, lord,’ I said. In fact, I had my doubts. The odds were long, and if we won, and Parmenio led us – well, I’ve said before that Alexander’s popularity with the troops was based on godlike demeanour and unbroken victory.

‘My battle!’ he said, and his eyes rolled back in his head.

Parmenio took the Thracians, all the light cavalry and his precious Thessalians and rode east. I should have gone, but Thaïs convinced me that Parmenio meant to kill Alexander with poison. Or that, rather, it was possible enough to warrant caution. But the king drank only water and ate only bread, and I didn’t see how he was getting poison.

Five days of this and the king was obviously losing weight, and his stomach had swelled in an odd and very bad way. His gut hurt all the time. He didn’t scream, but he lay on his camp bed and made grunting noises when he thought we couldn’t hear him.

He insisted on hearing every report, so that he knew that Darius was marching towards us by easy stages, a confident commander eager for battle, and that Parmenio had seized Issus.

There are only two passes over the mountains on to the plains of Cilicia from the headwaters of the Euphrates – the way the Great King was marching. To the north, there are the Amanic Gates, a good pass even for a large army and to the south, there is the pass of the Syrian Gates. Parmenio put scouting forces into both passes and then lay in wait at the Pinnacle of Jonah to see what Darius would do.

The news that Darius had a pontoon bridge over the Euphrates drove the king into a fever. He raged at his doctors, and none of them could agree what was wrong with him or how to fix it. And as more and more men suspected poison, the Greek doctors grew more and more afraid to take any action.

When Darius was estimated at five days’ march away, Parmenio came back for the army. He had the Great King where he wanted him, and he was ready to set his battlefield. He gathered all of us in the command tent, and laid out his plans of march. Like most of his plans, it was a simple one.

He was going to take the army to the Pinnacle of Jonah, with tripwire forces in both passes, and wherever the Great King went, Parmenio was going to meet him – in the pass where his superior numbers would be no match for our superior infantry.

I raised my hand. ‘Why would he fight us under those conditions?’ I asked.

‘Why does your foreigner do anything? Pride, foolish pride, young Ptolemy.’ Parmenio nodded. ‘Anyone else?’

Then he sent all the cavalry commanders away – except his sons. He kept Craterus and Philotas and Nicanor and Perdiccas, because this was to be an infantry fight.

I didn’t like it. I didn’t like the secret meeting, and I didn’t like the notion that Darius was a fool and would dance to our tune.

I went to the king’s tent, and found the king’s own physician, Philip of Arcarnia.