No matter which exact sea level they chose to display on the maps, a big southern arm of the ocean was going to cover Isidis Planitia, which was lower than most of Vastitas. And aquifers in the highlands around Isidis were being pumped down into it as well. So a big bay was going to fill the old plain, and because of that, construction crews were building a long dike in an arc around Burroughs. The city was located fairly close to the Great Escarpment, but its elevation was just below the datum. It was therefore going to become a port city every bit as much as Odessa, a port city on a world-wrapping ocean.

The dike they were building around Burroughs was two hundred meters high and three hundred meters wide. Maya found the concept of a dike to protect the city disturbing, though it was clear from the aerial shots taken of it that it was another pharaonic monument, tall and massive. It ran in a horseshoe shape, with both its ends up on the slope of the Great Escarpment, and it was so big that there were plans to build on it, to make it into a fashionable Lido district, containing small boat harbors on its water side. But Maya remembered once standing on a dike in Holland, with the land on one side of her lower than the North Sea on the other side of her; it had been a very disorienting sensation, more unbalancing than weightlessness. And, on a more rational level, as news programs from Earth now showed, all dikes there were currently, stressed by a very slight rise in sea level, caused by global warming initiated two centuries before. As little as a meter’s rise endangered many of the low-lying areas of Earth, and Mars’s northern ocean was supposed to rise in the coming decade by a full kilometer. Who could say whether they would be able to fine-tune its ultimate level so accurately as to make a dike sufficient? Maya’s work in Odessa made her worry about such control, though of course they were trying for it themselves in Hellas, and thought that they probably had it. They had better, as Odessa’s location gave them little margin for error. But the hydrologists also talked about using the “canal” that had been burned by the aerial lens before its destruction, as a runoff into the northern ocean, if such a runoff became necessary. Fine for them, but the northern ocean would have no such recourse.

“Oh,” Diana said, “they could always pump any excess up into Argyre Basin.”

• • •