Twitter turns four today. Co-founder Jack Dorsey made the first tweet on March 21, 2006, at 8.50pm (PST).

Happy Birthday Twitter (Four Years Old Today!)

Note the status number at the end of the URL of that tweet – twenty. Status numbers tell us the actual number of the post on the system. Wonder what happened to tweets one through nineteen? Maybe the content was so racy and damaging that they were quickly pulled before Twitter went live?

(Or, perhaps more likely, they were used for testing purposes.)

Happy birthday Twitter!