If we build it, they won't come

President Bush says he's committed to putting up 700 miles of steel fencing along the border between the U.S. and Mexico. He says we need such a barrier to stop terrorists and illegal immigrants from sneaking into the United States.

Of course, the idea of walling oneself off isn't a new one. For thousands of years, people have been building fences and moats and anything else they could think of - all in hopes of keeping some people in and some people out.

Reporter Nikki Tundel recalls some of history's most memorable walls and looks at just how effective they were.

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