The Forgotten Battle.

Raymond Ibrahim recalls the anniversary of the beginning of the 717-18 Siege of Constantinople, the second such Arab effort to break Christendom's bulwark. The focus on the Coptic deserters from the Muslim army is especially helpful.

Here's an earlier post of mine on the first siege, with invaluable insights from Ostrogorsky.  

A couple of thoughts:

1. Take the claimed numbers with a grain of salt. Medieval chroniclers, regardless of religion, tended to exaggerate in that department. Not as bad as their classical forebears, but still. 

2. Ibrahim is dead on when he says it deserves more press than Tours. Tours was important, but I'd argue that it wasn't the most important battle Martel fought against the Caliphate: his later southern campaign which led to the uprooting of Muslim France was more important.