“Byzantium – The Lost Empire” is a great documentary, written and directed by John Romer, produced by the Discovery Channel. Some parts of it, like the start above, are available online to watch, but you can also find it complete in p2p networks, or, in a high quality dvd release. The whole work includes three main chapters with the titles: 1) Building the Dream – 2) Heaven on Earth – 3) Forever and Ever.
If you wanted to see just one documentary on Byzantium, this would be the definite choice. Based on accurate historical information, is also filmed with passion and care.