Walls of Constantinople in the context of "Historic Areas of Istanbul"

In 717–718, Constantinople, the capital of the Byzantine Empire, was besieged by the Muslim Arabs of the Umayyad Caliphate. 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. In 716, after years of preparations, the Arabs, led by Maslama ibn Abd al-Malik, invaded Byzantine Asia Minor. The Arabs initially hoped to exploit Byzantine civil strife and made common cause with the general Leo III the Isaurian, who had risen up against Emperor Theodosius III. Leo, however, deceived them and secured the Byzantine throne for himself.

After wintering in the western coastlands of Asia Minor, the Arab army crossed into Thrace in the early summer of 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 partly 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. In spring 718, two Arab fleets sent as reinforcements were destroyed by the Byzantines after their Christian crews defected, and an additional army sent overland through Asia Minor was ambushed and defeated. Coupled with attacks by the Bulgars on their rear, the Arabs were forced to lift the siege on 15 August 718. On its return journey, the Arab fleet was almost completely destroyed by natural disasters.

Heraclius (Greek: Ἡράκλειος, romanized: Hērákleios; c. 575 – 11 February 641) was Byzantine emperor from 610 to 641. His rise to power began in 608, when he and his father, Heraclius the Elder, the Exarch of Africa, led a revolt against the unpopular emperor Phocas.

Heraclius's reign was marked by several military campaigns. The year Heraclius came to power, the empire was threatened on multiple frontiers. Heraclius immediately took charge of the Byzantine–Sasanian War of 602–628. The first battles of the campaign ended in defeat for the Byzantines; the Persian army fought their way to the Bosphorus but Constantinople was protected by impenetrable walls and a strong navy, and Heraclius was able to avoid total defeat. Soon after, he initiated reforms to rebuild and strengthen the military. Heraclius drove the Persians out of Asia Minor and pushed deep into their territory, defeating them decisively in 627 at the Battle of Nineveh. The Persian Shah Khosrow II was overthrown and executed by his son Kavad II, who soon sued for a peace treaty, agreeing to withdraw from all occupied territory. This way peaceful relations were restored to the two deeply strained empires.

Fatih (Turkish pronunciation: [ˈfaːtih]) or the Historical peninsula (in Turkish: Tarihi Yarımada), is a municipality and district of Istanbul Province, Turkey. Its area is 15 km, and its population is 368,227 (2022). It is home to almost all of the provincial authorities (including the mayor's office, police headquarters, metropolitan municipality and tax office) but not the courthouse. It encompasses the historical peninsula, coinciding with old Constantinople. In 2009, the district of Eminönü, which had been a separate municipality located at the tip of the peninsula, was once again remerged into Fatih because of its small population. Fatih is bordered by the Golden Horn to the north and the Sea of Marmara to the south, while the Western border is demarked by the Theodosian wall and the east by the Bosphorus Strait.

Constantinople was besieged by the Arabs in 674–678, in what was the first culmination of the Umayyad Caliphate's expansionist strategy against the Byzantine Empire. Caliph Mu'awiya I, who had emerged in 661 as the ruler of the Muslim Arab empire following a civil war, renewed aggressive warfare against Byzantium after a lapse of some years and hoped to deliver a lethal blow by capturing the Byzantine capital of Constantinople.

As reported by the Byzantine chronicler Theophanes the Confessor, the Arab attack was methodical: in 672–673 Arab fleets secured bases along the coasts of Asia Minor and then installed a loose blockade around Constantinople. They used the peninsula of Cyzicus near the city as a base to spend the winter and returned every spring to launch attacks against the city's fortifications. Finally the Byzantines, under Emperor Constantine IV, destroyed the Arab navy using a new invention, the liquid incendiary substance known as Greek fire. The Byzantines also defeated the Arab land army in Asia Minor, forcing them to lift the siege. The Byzantine victory was of major importance for the survival of the Byzantine state, as the Arab threat receded for a time. A peace treaty was signed soon after, and following the outbreak of another Muslim civil war, the Byzantines even experienced a brief period of ascendancy over the Caliphate. The siege was arguably the first major Arab defeat in 50 years of expansion and temporarily stabilized the Byzantine Empire after decades of war and defeats.

The Hodegon Monastery (also Monastery of the Panaghia Hodegetria or Monastery of the Hodegoi) in Constantinople was allegedly founded by Saint Pulcheria (399–453), a daughter of Emperor Arcadius. The monastery is considered one of the three main Marian foundations built in the city along with the Blachernai and the Chalkoprateia.

The monastery was situated beyond the Chalkoprateia by the sea and served as the counterpart of the Blachernai so that these structures bracket the city of Constantinople as well as the processions such as the weekly Blachernai procession that began at the Theodosian walls and ended at Chalkoprateia. However, the exact location of the monastery is still subject to discussion. The Hodegon Monastery is believed to be named after the term hodegoi, which referred to the guides who led the blind toward the miraculous well within the structure.

The Basilic or Basilica cannon, i.e. 'royal gun', as the Greeks called it, also known as Urban's cannon or the Ottoman Cannon was a very large-calibre cannon designed by Orban or Urban, a Hungarian cannon engineer, at a time when cannons were still new. It is one of the largest cannons ever built.

The cannon was first offered in 1452 to Byzantine emperor Constantine XI, who was not able to bring up the sum required for its construction. It was then offered to the Ottoman Sultan Mehmed II, who ordered the cannon built after learning that it could smash through walls using a large projectile. Huge amounts of scrap bronze were needed in order to cast the 27 ft (8.2 m) long cannon, with 8 in (200 mm) thick walls. When it was completed, the cannon was used by the Ottoman Army during the 1453 siege which led to the fall of Constantinople, and played a key role in damaging the city walls. It was one of a total of some 70 guns built by Orban for Mehmed.