Constantinople

Constantinople was THE city during the Middle Ages in Europe.

From the mid-5th century to the early 13th century, Constantinople was the largest and wealthiest city in Europe.

As the largest and wealthiest city in Europe during the 4th–13th centuries and a center of culture and education of the Mediterranean basin, Constantinople came to be known by prestigious titles such as Basileuousa (Queen of Cities) and Megalopolis (the Great City) and was, in colloquial speech, commonly referred to as just Polis (ἡ Πόλις) ‘the City’ by Constantinopolitans and provincial Byzantines alike.

https://en.wikipedia.org/wiki/Constantinople

The city was considered to be the “Holy Chapel” to house the greatest relics.

However, the concept of a ‘Holy Chapel’, built to contain the most
sacred relics of Christendom within the residence of the most powerful Christian ruler, lived on for centuries.

By the end of the twelfth century, the church was renown as
the home of some of the most important relics of Christendom: the Mandylion of Christ,
the Holy Keramion, the Crown of Thorns, the Holy Nail, Christ’s iron collar shackle, the
linen sheets in which his body was wrapped in the tomb, the linen towel with which he
dried the apostle’s feet, the Holy Lance, Christ’s purple robe, the reed which he held in
his right hand, Christ’s leather sandals, and a piece from his tomb stone.

https://arthistory.columbia.edu/sites/d … monies.pdf

Constantinople was impenetrable for 900 years until the Fourth Crusade.

Although besieged on numerous occasions by various armies, the defenses of Constantinople proved impenetrable for nearly nine hundred years.

In 1204, however, the armies of the Fourth Crusade took and devastated the city and, for several decades, its inhabitants resided under Latin occupation in a dwindling and depopulated city.

https://en.wikipedia.org/wiki/Constantinople

The timing of the Middle Ages is directly associated with the rise and fall of Constantinople. When Rome fell in 476, Constantinople remained as the only seat of the Roman government and marked the beginning of the Middle Ages. The Middle Ages ended when Constantinople fell in 1453 to the Ottoman empire.

In the history of Europe, the Middle Ages or medieval period (also spelled mediæval or mediaeval) lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire in 476 and transitioned into the Renaissance and the Age of Discovery.

https://en.wikipedia.org/wiki/Middle_Ages

“The city was finally besieged and conquered by the Ottoman Empire in 1453, remaining under its control until the early 20th century, after which it was renamed Istanbul under the Empire’s successor state, Turkey.”
https://en.wikipedia.org/wiki/Constantinople