Free In Great Waters by Kit Whitfield

children became the royal houses of Europe,” he said. “She had many children. And she found landsmen she wished to favour, and found them deepsmen brides, to have more children, to marry her own.”
    “Brides?” That wasn’t a word Henry had heard before; it certainly didn’t sound like anything the deepswomen did.
    “Wives.” Two words for one thing was an annoyance Henry wasalready used to, but he wasn’t pleased to find it applied to his own people. “There have to be children, but brothers and sisters—children with the same mother and father—cannot marry. Their children get ill, come out wrong.”
    Henry thought about that. The complexities of adult courtship had been beyond him while he lived in the sea; he’d seen the dances, the woman and man spiralling each other, crooning and trying to impress, but how they’d chosen each other in the first place was not something he’d considered. Now Allard mentioned it, he was right: brothers and sisters did not mate. Deepsmen with too many sisters would sometimes leave the tribe, go and join another.
    “Angelica’s children could not marry each other,” Allard said. “She lived a long time. The Venetians did not want her children to be princes in other countries: they did not want princes in other nations who could challenge them. But Angelica made it happen. When Venice would not agree, she went into the sea for two months and would not come back. She said that nations could have her children and grandchildren, that she would see to the breeding of deepsmen kings, if they would submit themselves to the Venetian Empire. That the Empire would be ruled by brothers, and would be strong. But that this was her will, and if her people would not submit to it, she would not protect them. She went away, and when she came back, the Venetians agreed. And she was right. She built a great empire, and while she was alive, it held together. Angelica was an extraordinary queen, there has never been a queen like her. But after she was dead, there were wars.”
    “No.” Henry did not know how to express the feeling, but the idea of Angelica being dead rather upset him. She had sounded strong, victorious. Death, as Henry had witnessed it, was a matter of defeat; strong deepsmen stayed alive.
    “There were wars, Henry. Angelica had favoured her most loyal men, chosen them to go out into the canals and—and marry with deepswomen. Their children married her children, those children were kings. But when she was gone, there was no one to choose who would have deepsmen brides and who would not. Men fought for the right, tried to take brides in secret, would not accept children born tothe wrong men. There was no order without Angelica, and men killed each other, sent assassins and held battles. Nobles fought for the right to decide who would have deepsmen children and who would not, and they sent soldiers, battles on land, where the deepsmen could not help. The world grew dark, it was a terrible time.”
    This was harder to follow: landsmen tended to care about strange things, so following why they’d be angry was an uncertain business. It sounded like a power struggle, but back home such fights only happened with children that already existed. A mother might lash out at another tribeswoman who threatened her baby; fighting over children not yet born was bewildering. Possibly Allard was talking about mating fights, but the idea seemed strange: what was the point of landsmen having mating fights over deepswomen, fighting on land where the deepswomen couldn’t see them? Such a man was likely to find himself with an unconvinced mate, Henry considered, and would have endangered himself for nothing.
    “What bastard?” he said, returning to the important point.
    “I am coming to that, Henry,” Allard said. “After too many wars, the Venetian Empire started to fall. China went its own way, the Arab princes made treaties with their own tribes of deepsmen to protect their traders