This refers to historical accuracy, and the accident was on my part.
Awhile ago, somebody was talking about undergoing a city sized mega project, and the idea of making a city like Venice came up. I decided that I really liked that idea, so I started working on an aboveground city with canals and roads and stone buildings. I should probably add wood to the buildings too, and there's a problem with me building roads between the canals and most buildings but that's not the point. What's important is defense. I decided that with such a large city, the issue of enemies would be rather major. Ideally I would eventually have a few groups of melee infantry. Everybody else would be crossbowmen who had active duty a couple months a year or so. Split into groups of 10, the maximum size. Today, I was looking up Venician history on Wikipedia. "By 1303, crossbow practice had become compulsory in the city, with citizens training in groups." They were also apparently organized into units of 12, which is slightly higher than what I can do, but still close. There is no way I can turn away from that idea now, despite how hard it is to get dwarves to train with crossbows right now.
There's a lot more I could do to make it accurate, but I'm not about to dig under every house to build wood logs and then flood that layer.