The Siege of Constantinople in 717 was a helluva more important than Tours (which has been overrated ever since Gibbon). Just think about it:

The greatest city in the world, with its riches, strategic, and symbolic importance vs. a relatively backward country filled with “unwashed barbarians”.

Why did the Umayyads, Abbasids, and Sejulks keep pushing into Asia Minor for all those years, but not past the Pyrenees after their initial attempts?

On topic, the Byzantine Empire is one of my favorite civilizations and periods along with the Hellenistic Era and Rise of Roman Republic, and The Bronze Ages.

Byzantines were a great and fascinating civilization.