Here's a cool little illustration of the history of advertising, the advertising timeline dates back to 2000BC when Egyptians first invent outdoor advertising by carving public notices in steel, to the year 2011 where online advertising worldwide becomes second in budget priority, typically at the expense of print and radio.
The illustration was created by/for InfoLinks, you know the ad company that places pop-up in-text ads.
I know there may be some disagreement with the info-graphic on dates and who did what and when, either way it's a fun illustration of where advertising has been.