626: The siege of Constantinople in 626 was both the culmination of the last great Roman-Persian War and the first of centuries' worth of large-scale attacks on the New Rome. The Sasanians had marched from their homelands in Mesopotamia and the Iranian Plateau all the way to the Asian side of the Straits, while the Persians' powerful European allies, the Avars and affiliated Slavic peoples, assaulted the city on the European side. But the city was defended by a strong and adequately provisioned garrison, while the Roman fleet precluded effective cooperation between the two besieging armies. The Avar artillery apparently barely made a dent in Constantinople's walls, and eventually both armies retreated.
654-655: With the death of Yazdgird III in 652, the Arabs felt ready to "take Constantinople and exterminate that kingdom as well." The idea (as in later Arab campaigns) was that the Arabs would march across Anatolia to Chalcedon (directly opposite Constantinople), while the fleet would sail into the Aegean. Mu'awiya, governor of Syria, constructed a large fleet from the conquered portions of the Mediterranean, including specially small ships that "rapidly dart to and fro over the waves of the sea around the very large ships." After some delays, the Arab armada crushed the Byzantine navy (the Battle of Phoenix, or of the Masts), nearly captured the emperor, and moved north against Constantinople. Fortunately, says a contemporary Armenian writer, a storm destroyed the Arab fleet and without naval support, the Arab army at Chalcedon was forced to retreat. An Arab army attempted to salvage some honor by attacking Caesarea in Cappadocia, but the Romans defeated them there as well.
667-670 (674-678): Mu'awiya's second attempt at taking Constantinople, and now as Caliph. The Caliph had sent troops to support an Armenian rebel against Byzantium, but when the rebel was executed by the Byzantines it was decided that the army should just be used to try and conquer Rome again. Reinforcements were sent into Anatolia and a fleet was made ready, and by 668 the Arabs were blockading Constantinople from Chalcedon on the Asian side and Thrace/Cyzicus on the European side. Ultimately the Arab fleet was forced back by the new invention of Greek fire and by Byzantine reinforcements from the central Mediterranean, while the army at Chalcedon left when "they could no longer bear the pain of hunger and pestilence."
Wikipedia suggests this siege happened in the 670s, but modern scholarship (In God's Path by Robert G. Holland, for example) generally takes the stance that the siege did indeed happen in the 660s and the 670s dating is a "historiographical misunderstanding" (e.g. a contemporary source has someone saying that they still have Thomas II of Constantinople's letter to the Pope, which he couldn't send because the Arabs were besieging the city throughout his entire reign). Marek Jankowiak's 80-page article "The First Arab Siege of Constantinople" is a good place to start.
717-718: Probably the most famous Arab siege. AH 100 being AD 718, many Muslims may have felt confident that this time, finally, Rome would fall. After all, Caliph Sulayman even said "I shall not cease from the struggle with Constantinople until either I conquer it or I destroy the entire dominion of the Arabs in trying." But despite the 5,000 ships that were mobilized and the thousands of volunteers, the capable defense of Leo III, including the destruction of roads and the scorching of the earth, deprived the besiegers of supplies, forcing the Arabs to begin eating feces. Even worse, "so much snow fell that the ground was made invisible for a hundred days," while the fire-bearing Roman fleet successively shattered its Arab counterparts. Not even the surviving Arabs safely returned home, a storm devastating the returning fleet.
654-655: With the death of Yazdgird III in 652, the Arabs felt ready to "take Constantinople and exterminate that kingdom as well." The idea (as in later Arab campaigns) was that the Arabs would march across Anatolia to Chalcedon (directly opposite Constantinople), while the fleet would sail into the Aegean. Mu'awiya, governor of Syria, constructed a large fleet from the conquered portions of the Mediterranean, including specially small ships that "rapidly dart to and fro over the waves of the sea around the very large ships." After some delays, the Arab armada crushed the Byzantine navy (the Battle of Phoenix, or of the Masts), nearly captured the emperor, and moved north against Constantinople. Fortunately, says a contemporary Armenian writer, a storm destroyed the Arab fleet and without naval support, the Arab army at Chalcedon was forced to retreat. An Arab army attempted to salvage some honor by attacking Caesarea in Cappadocia, but the Romans defeated them there as well.
667-670 (674-678): Mu'awiya's second attempt at taking Constantinople, and now as Caliph. The Caliph had sent troops to support an Armenian rebel against Byzantium, but when the rebel was executed by the Byzantines it was decided that the army should just be used to try and conquer Rome again. Reinforcements were sent into Anatolia and a fleet was made ready, and by 668 the Arabs were blockading Constantinople from Chalcedon on the Asian side and Thrace/Cyzicus on the European side. Ultimately the Arab fleet was forced back by the new invention of Greek fire and by Byzantine reinforcements from the central Mediterranean, while the army at Chalcedon left when "they could no longer bear the pain of hunger and pestilence."
Wikipedia suggests this siege happened in the 670s, but modern scholarship (In God's Path by Robert G. Holland, for example) generally takes the stance that the siege did indeed happen in the 660s and the 670s dating is a "historiographical misunderstanding" (e.g. a contemporary source has someone saying that they still have Thomas II of Constantinople's letter to the Pope, which he couldn't send because the Arabs were besieging the city throughout his entire reign). Marek Jankowiak's 80-page article "The First Arab Siege of Constantinople" is a good place to start.
717-718: Probably the most famous Arab siege. AH 100 being AD 718, many Muslims may have felt confident that this time, finally, Rome would fall. After all, Caliph Sulayman even said "I shall not cease from the struggle with Constantinople until either I conquer it or I destroy the entire dominion of the Arabs in trying." But despite the 5,000 ships that were mobilized and the thousands of volunteers, the capable defense of Leo III, including the destruction of roads and the scorching of the earth, deprived the besiegers of supplies, forcing the Arabs to begin eating feces. Even worse, "so much snow fell that the ground was made invisible for a hundred days," while the fire-bearing Roman fleet successively shattered its Arab counterparts. Not even the surviving Arabs safely returned home, a storm devastating the returning fleet.