Rivers are some of the most difficult obstacles to cross. Rivers are often deep and swift-flowing, and many have steep banks. Because of these difficulties, people, as well as wild animals, have looked for the easiest places to cross.

On a river bend, one side will have a gentle slope, and so may seem to be an easy place to cross. But the other side will always be very steep, and it will be very difficult to get out.

The best place to cross a river is where the river is straight, for both banks are then likely to be moderately steep.

The other thing to remember is that most rivers today - except in wilderness areas - are not at all like they were when the first people started crossing them. For example, many places have names ending in 'ford'. That tells you it was an easy place to cross. At the time the first people crossed, the river would have been wide and shallow, like the picture above. But over the centuries people have changed the river, often by building over the banks and making the river narrower, so that there is now no sign of a wide, shallow place.

One of the most remarkable changes is in London, England. When the Romans saw the river 2000 years ago, it was wide and shallow with many islands. That is why they were able to cross it. In fact it was THREE times wider than it is today. Now it is narrow, and so it flows faster. The bed has also been dredged, to that it is deeper. It would be impossible to walk across today. Of course, it doesn't matter much because rivers are crossed by bridges, and because rivers are narrower than they were, bridges can be shorter, and less costly, too.

Good river crossings are still few and far between. So they are often places where people built villages, towns and cities. Because you can cross rivers at so few points, they are important in times of war, and in the past, most crossings were protected by forts and castles.