The Second Arab Siege of Constantinople: A Macrohistory (Day Twenty-One)

So, today's featured article on Wikipedia showcases the macrohistorical import of a given event.

The Second Arab siege of Constantinople in 717–718 "was a combined land and sea offensive by the Muslim Arabs of the Umayyad Caliphate against the capital city of the Byzantine Empire, Constantinople. The campaign marked the culmination of twenty years of attacks and progressive Arab occupation of the Byzantine borderlands, while Byzantine strength was sapped by prolonged internal turmoil."

After wintering in the western coastlands of Asia Minor, the Arab army crossed into Thrace in early summer 717 and built siege lines to blockade the city, which was protected by the massive Theodosian Walls. The Arab fleet, which accompanied the land army and was meant to complete the city's blockade by sea, was neutralized soon after its arrival by the Byzantine navy through the use of Greek fire. This allowed Constantinople to be resupplied by sea, while the Arab army was crippled by famine and disease during the unusually hard winter that followed.

The second Arab siege of Constantinople was far more dangerous for Byzantium than the first as, unlike the loose blockade of 674–678, the Arabs launched a direct, well-planned attack on the Byzantine capital, and tried to cut off the city completely from land and sea.... The Arab failure was chiefly logistical, as they were operating too far from their Syrian bases, but the superiority of the Byzantine navy through the use of Greek fire, the strength of Constantinople's fortifications, and the skill of Leo III in deception and negotiations also played important roles.

The writing of history occurs through erasing possible future narratives, and most of the time, just few hurdles against one and a few breaks for another will suffice sketch a plot.  

The outcome of the siege was of considerable macrohistorical importance. The Byzantine capital's survival preserved the Empire as a bulwark against Islamic expansion into Europe until the 15th century, when it fell to the Ottoman Turks. Along with the Battle of Tours in 732, the successful defense of Constantinople has been seen as instrumental in stopping Muslim expansion into Europe. As military historian Paul K. Davis wrote, "By turning back the Moslem invasion, Europe remained in Christian hands, and no serious Moslem threat to Europe existed until the fifteenth century. This victory, coincident with the Frankish victory at Tours (732), limited Islam's western expansion to the southern Mediterranean world." ...Consequently, military historians often include the siege in lists of the "decisive battles" of world history.