Hate to contradict you feanaaro, especially about Rome, but I think the original city may have had streams among its hills. I studied Roman history a few years ago, and remember learning that the early settlers had problems with flooding (in the low areas) and drainage. The first villages were located in the hills as a result, and a major early project was the Cloaca Maxima. Any streams that may have existed then will be covered as the city expands. I am uncertain about whether there were any real rivers in early Rome, but I do know that London had numerous small rivers that have been subsequently buried by urban development. You might be surprised, is all I'm saying.

If your river is meant to be so large, I think I know the perfect example for you to work from. The Yenisei in northern Russia has a huge watershed, and numerous islands along its course. Try checking it out in GoogleEarth ( I just did, and recommend the area around 69-70 degrees N and 84-85 degrees E).