I took my Hetaeroi south and east, on to the broad, dry, dusty Cappadocian Plain. We moved fast, with no baggage, and we slept under the stars, with saddlecloths for pillows. Thaïs’s beautiful skin grew tanned, and she claimed that it would ruin her complexion, but she was developing a new persona, Thaïs the Amazon, and her Angeloi were developing into a miniature Prodromoi, complete with spears and swords. Our daughter had her second birthday in Asia, carried on a mule.

I had Philotas to my south and Kineas, of all people, to my north, and we swept east and south, looking for enemies and for news.

In every town, either Thaïs had people, in which case they reported to her, or she didn’t, in which case her Angeloi bought some. And she was teaching us – a few of us, Calchias of the Prodromoi and the Paeonian commander, Ariston and Cleander, from the so-called mercenary cavalry. Teaching us to use this network of spies carefully, to integrate it into our scouting. Thaïs knew a little of how to handle a cavalry patrol, and none of us knew how to suborn a town official, but together we made a powerful combination – the more so as we learned from each other.

As an example of how this might work, let me offer the race across the Plain of Cappadocia. It was Parmenio’s operation – remember, the king was still in Ankyra, and was determined not to march until he could move all the way to the Cilician Gates with his flanks covered. Given that we were abandoning our communications with Macedon, this seemed sensible.

I had the middle route – south from Ankyra, then south-east along the axis Gorbeus–Mazaka. I was confident that this would be the army’s actual route, but by sending Philotas along the southerly route and Kineas along the northerly route, we spread the most confusion and we gave the king options in the event of logistical or political troubles – water shortage, or hostile tribes.

On the second night, three of my best rode into Gorbeus with Strako and a half-dozen of the Angeloi – the town was six days by pack train from Ankyra, and still imagining itself safe from us. The next morning at dawn, Thaïs’s friends opened the gates and my whole squadron came in at a canter, raising dust all the way. The garrison – forty Persian archers under a drunken aristocrat – surrendered on the spot.

That’s how it was supposed to work. But the news was all good – the satrap of Cilicia had only three hundred men in the Cilician Gates. Arsames was raising his men on the other side of the barrier. Thaïs’s people said he was considering outright surrender.

‘Oh, if I were a man,’ she said bitterly. ‘Someone should go.’

We sent Polystratus with the former garrison commander’s signet ring and an offer – a thousand talents of gold to let us have the Gates without a fight. It was insanity – the gates were a hundred and fifty stades of goat tracks that even Persian levies could hold against us – but it was always worth trying Thaïs’s way.

In the morning, we were off across the parched plain, all volcanic rock and thin soil and people living so close to starvation that the girls were old hags at twenty-five and the men looked like bent-over old men.

I lost touch with Philotas and pushed on. A day out of Gorbeus, and there was no more water. Nor local people to help us.

We pushed on. Our canteens were full and we had packhorses. My two-year-old squawked a lot – she wanted more water than we had to give her.

Thaïs and I had the worst fight of our lives. She told me that I was a typical man and a poor father, because I would not send her back to the last water source with a detachment. I couldn’t spare the troopers, and she knew it.

For the first time I could remember I slept alone that night, and it was cold.

And my mouth was dry, for several reasons. I slept badly. I considered what would happen if my daughter died in the waste. What would die with her. How much I loved Thaïs.

In the morning I made her a public apology, and sent Polystratus’s sidekick Theodore and twenty men back to Gorbeus with Thaïs and our child. I was selfish. I loved being out on patrol with Thaïs, and at some remove I was jealous of the daughter that seemed to take up all her time.

But the desert is full of tests, and Thaïs kissed me before she left. ‘You are better at admitting you are wrong then most men,’ she said.

North of Mazaka, we ran into our first Persian cavalry patrol. They were good, and they’d laid an ambush for us at a waterhole. We, on the other hand, were exhausted and our horses were done in.

But we’d been fighting Memnon. No one gets sloppy against a master. The Angeloi – men dressed in local cloth, riding local horses – picked up the ambush a day in advance.

I triggered it myself, with fifty men in full armour, heads down against the sun. We rode over the ridge that defined the northern edge of the watered area and they hit us immediately. Poseidon was so far done that he ignored the fight and went for the water, which we could see – blue as blue in the distance.

We lost two men. I got Poseidon to see reason with some hard kicks to his ribs, and we turned into the attackers, most of whom had bows. They were shooting our horses, trying to dismount us for easy capture.

Then Pyrrhus appeared behind them with the rest of my force, and they didn’t stop to think about it. They were well trained. As soon as they saw their ambush broken, every one of them broke contact, changed horses and they were gone. We killed six and captured four more, all wounded.

We lost over a dozen precious horses and got none in return.

I didn’t bother pursuing them. They were desert men themselves, and I expect that they had a second ambush pre-prepared. I would have.

I was very cautious moving up to Mazaka, but I didn’t make another contact. Thaïs’s resident there refused to meet any of us – there’s the real world of spies, afraid of their own shadows – but a small boy brought us two parchments, covered in dense Aramaic, and one of my grooms, a Babylonian Jew named Jusef, read it well enough. It was an itinerary of the Cilician Gates, with notes of distance and troop locations, and it was just ten days old.

I sent it back to the king with Pyrrhus and ten troopers, and then I sat in Mazaka and waited for Philotas. He came up the next day, and I was happy to see him, and he to see me. Things are different, once the fur begins to fly.

Kineas was four more days, and all his horses looked as if they were going to die. He’d gone as far east as Tyana and had made two contacts with the Persian scouts coming over the mountains from the Euphrates Valley, far to the east. The Persians were closer than we hoped, though farther than our worst fears. Just like war.

Philotas wanted to go for the Gates with five or six hundred horse, but I restrained him gently. I appealed to his fear of failure.

The king crossed the desert in three days. He did it with night marches – always easier in the desert – and forward stores of water.

When he was a day away and we were in contact with the Prodromoi, Polystratus came back with a gold ring and a promise.

‘He’s a right bastard, and that’s no mistake, lord,’ Polystratus said. ‘He wants to play both sides – said he won’t openly go against the Great King, but that he’ll keep all but his advance guard out of the Gates and it’s up to us to get through them.’ Polystratus shrugged. ‘And that’s what we get for a thousand talents.’

But Alexander agreed like a shot, and then he sent the Thracians, the Agrianians and a company of hypaspitoi through the gates. The Cretan archers and the Macedonian crossbowmen moved along the high ground, slowly but thoroughly, and the Thracians tripped anything they came across, and the army marched in behind us – I was with the archers. Alexander was so confident that the advance guard didn’t even leave a day in advance. We moved at a slow walking pace, and we surprised the poor bastards at the break of the second day. It was red slaughter, professionals against amateurs. When the Thracians broke them, the Agrianians harried them along the ridges and the archers shot them down.