So as Zeyk’s Arabs drove the boxes of masks to West, Southwest, and South gates, there were huge crowds already congregating inside each of them, everyone dressed either in walkers with heating filaments, or in the heaviest clothes they had — none too heavy for the job at hand, Nadia judged as she went in Southwest Gate, and passed out facemasks from boxes. These days many people in Burroughs went out on the surface so seldom that they rented walkers to do so. But there were not enough walkers to dress everyone, and they had to go with people’s interior coats, which were fairly lightweight, and usually deficient in headgear. The message about the evacuation had been sent out with a warning to dress for 255°K, however, and so most people were layered in several garments, appearing thick-limbed and thick-torsoed.

Each gate lock could pass five hundred people every five minutes — they were big locks — but with thousands of people waiting inside, and the crowds growing as Saturday morning wore on, it was not anywhere near fast enough. The masks had been distributed through the crowds, and it seemed certain to Nadia that at this point everyone had one. It was unlikely that anyone in the city was unaware of the emergency. And so she went around to Zeyk, and Sax, and Maya and Michel, and all the other people she knew that she saw, saying, “We should cut the tent wall and just walk out. I’m going to cut the tent wall now.” And no one disagreed.

Finally Nirgal showed up, gliding through the crowd like Mercury on an urgent errand, smiling hugely and greeting acquaintance after acquaintance, people who wanted to hug him or shake his hand or just touch him. “I’m going to cut the tent wall now,” Nadia told him. “Everyone has masks, and we need to get out of here faster than the gates will let us.”

“Good idea,” he said. “Let mejust announce what’s happening.”

And he jumped three meters into the ajr, grabbing a coping on the gate’s concrete arch and hauling himself up so that he was balanced on it, both feet on the same three-centimeter strip. He turned on a small shoulder loudspeaker he was wearing, and said, “Attention, please! — We’re going to start cutting the tent wall, right above the coping — there should be a breeze outward, not very strong — after that, people nearest the wall out first, of course — there will be no need to hurry at that point — we’ll cut extensively, and everyone should be out of the city in the following half hour. Be ready for the cold — it will be very invigorating. Please get your masks on, and check your seal, and the seal of the people around you.”

He looked down at Nadia, who had gotten a little laser welder out of her black backpack, and now showed it to Nirgalrholding it overhead so that much of the crowd could see it.

“Is everyone ready?” Nirgal asked over his loudspeaker. Everyone visible in the crowd had a white mask over their lower faces. “You look like bandits,” Nirgal told them, and laughed. “Okay!” he said, looking down at Nadia.

And she cut the tent.

Sensible survival behavior is almost as contagious as panic, and the evacuation was quick and orderly. Nadia cut about two hundred meters of tenting, right above the concrete coping, and the higher air pressure inside caused an outflowing wind that held the transparent layers of the tent fabric up and out from the coping, so that people could climb over the waist-high wall without having to deal with it. Others cut the tent near West and South gates, and in about the time it takes to empty a big stadium, the population of Burroughs was out of the city, and into the cold fresh air of an Isidis morning: pressure 350 millibars, temperature 261K°, or –12° Celsius.

Zeyk’s Arabs stayed in their rovers and served as escorts, rolling back and forth and guiding people up to the line of hillocks a few kilometers to the southwest of the city, called the Moeris Hills. Floodwater reached the eastern side of the city as the last part of the crowd made it onto this line of low bumps in the plain, and Red observers, ranging wide in rovers of their own, reported that the flood was now running north and south around the foot of the city wall, in a surge that at this point was less than a meter deep.

So it had been a very, very close thing; close enough to make Nadia shudder. She stood on the top of one of the Moeris hillocks, looking about trying to gauge the situation. People had done their best, but were insufficiently dressed, she thought; not everyone had insulated boots, and very few people had much in the way of headgear. The Arabs were leaning out of their rovers to show people how to wrap scarves or towels or extra jackets over their heads in improvised burnoose hoods, and that would have to do. But it was cold out, very cold despite the sun and the lack of wind, and the citizens of Burroughs who did not work on the surface were looking shocked. Although some were in better shape than others; Nadia could spot Russian newcomers by their warm hats, brought from home; she greeted these people in Russian, and almost always they grinned — “This is nothing,” they shouted, “this is good ice-skating weather, da?” “Keep moving,” Nadia said to them and to everyone else. “Keep moving.” It was supposed to warm up in the afternoon, perhaps up to freezing.

Inside the doomed city the mesas stood stark and dramatic in the morning light, like a titanic museum of cathedrals, the banks of windows inlaid in them like jewels, the foliage on the mesa tops little green gardens capping the redrock. The city’s population stood on the plain, masked like bandits or hay fever victims, bundled thickly in clothes, some in slim heated walkers, a few carrying helmets for use later if needed; the whole pilgrimage standing and looking back at the city: people on the surface of Mars, their-faces exposed to the frigid thin air, standing hands in their pockets, above them high cirrus clouds like metal shavings plastered against the -dark pink sky. The strangeness of the sight was both exhilarating and terrifying, and Nadia walked up and down the line of knobs talking with Zeyk, Sax, Nirgal, Jackie, Art. She even sent another message to Ann, hoping that Ann was receiving them, even though she never answered: “Make sure the security troops have no trouble at the spaceport,” she said, unable to keep the anger out of her voice. “Keep out of their way.”

About ten minutes later her wrist beeped. “I know,” Ann’s voice said curtly. And that was all.

Now that they were out of the city, Maya was feeling buoyant. “Let’s start walking,” she cried. “It’s a long way to Libya Station, and half the day is almost gone already!”

“True,” Nadia said. And many people had already started, heading over to the piste that ran out of Burroughs South Station, and following it south, up the slope of the Great Escarpment.

So they walked away from the city. Nadia often stopped to encourage people, and so quite often she was looking back at Burroughs, at the rooftops and gardens under the transparent bubble of the tent, in the midday sunlight — down into that green meso-cosm that for so long had been the capital of their world. Now rusty black ice-flecked water had run almost all the way around the city wall, and a thick flow of dirty icebergs was coming down from the low crease to the northeast, pouring toward the city in a broadening torrent, filling the air with a roar that raised the hair on the back of her neck, a Marineris rumbling…

The land they walked over was dotted by scattered low plants, mostly tundra moss and alpine flowers, with occasional stands of ice cactus like spiky black fire hydrants. Midges and flies, disturbed by the strange invasion, whirred around in the air overhead. It was noticeably warmer than it had been in the morning, the temperatures rising fast; it felt a little above zero. “Two seventy-two!” Nirgal cried when Nadia asked him in passing. He was passing by every few minutes, running up and down the crowd from one end of the line to the other and back again. Nadia checked her wrist: 272°K. The wind was very slight, and from the southwest. The weather reports indicated the high-pressure zone would stay over Isidis for another day at least.