Not exactly. When the Western Empire fell, the Eastern Empire retained Constantinople as its capital, from which it engaged in a protracted series of increasin

Not exactly. When the Western Empire fell, the Eastern Empire retained Constantinople as its capital, from which it engaged in a protracted series of increasingly expensive wars with the Sassanid Empire (modern-day Iran). These conflicts peaked in the early 7th century, at which point the Sassanids suffered an astonishing implosion. http://en.wikipedia.org/wiki/Sassanid_Empire http://en.wikipedia.org/wiki/Sassanid_Empire That was the vacuum that Islam (then nascent) filled. Only after seizing the remnants of Persia (and, critically, control of the silk routes running through it) could the first Caliphate move into territory once controlled by Constantinople. By the time the second Caliphate had extended Islam's control into Spain, more than four centuries had passed since the abandonment of Rome as a capital city (330 CE), after which the city persevered for another century before being sacked entirely. However the Western Empire was long gone by the time Islam appeared in the territory it once controlled. http://en.wikipedia.org/wiki/File:Map_of_expansion_of_Caliphate.svg http://en.wikipedia.org/wiki/File:Map_of_expansion_of_Caliph...