Zoos kept animals behind iron bars and concrete walls before Carl Hagenbeck thought of using moats to enclose animals.

Now African antelopes and lions appear to be in the same field although they are separated by a deep wide moat or gully.

Because a zoo can not approximate vast wild areas, zoo architects try to give animals a stimulating environment.

Zoos provide polar bears with fish in ice and slides so that the bears will feel at home.

Zoos also offer the public a view of animals as if they were living side by side in the wild.