On this day, May 11, 330 A. D., Constantinople was founded by Constantine I (the Great). The Eastern Roman or Byzantine Empire that he founded would last for 1,123 years and 11 days--until the reign of another Constantine--Constantine XI Palaeologus, the 88th Byzantine Emperor who died defending Constantinople from the Turks in 1453 (or the Byzantine year of 6961, because the Byzantines dated their calendar from the date of creation, which they believed was in 5508 B. C.)

Here is a nice picture that I found in another post of Constantine I:

There is a brief article about the founding of Constantinople and about Constantine I at About.com's "This Day in Medieval History" page. (I think it is significant that the only article for the day there is on Constantinople's founding!). The article can be found here:

Lastly, here is a nice map that I scanned showing the major buildings of Constantinople in 330 A. D.: