Constantinople held back “the east” from the west for nearly a thousand years. It was a fortress city with greater defences than any other on the planet at the time, including the famed Theodosion walls, a mighty curtain wall, although numerous towers and other defences protected the city as well.
https://en.m.wikipedia.org/wiki/Walls_of_Constantinople
The power of the once mighty eastern Roman’s however shrank back through centuries of war with the ottomans until a few miles from the walls was the only territory the eastern romans held. Finally a massive army of ottomans, said to be up 200,000 strong, faced off against a paltry force of 7,000 or so defenders, barely enough to man the walls. (Battle of Minas Tirith cough).
https://en.m.wikipedia.org/wiki/Fall_of_Constantinople
You can add the battle of Vienna to the inspirations however, the largest Calvary charge in history was western horsemen riding to the aid of the besieged imperial city of Vienna (again by the forces of countless thousands of ottoman orcs), when a heroic charge of 18,000 polish hussars and german knights ended ottoman encroachment into the west once and for all.
https://en.m.wikipedia.org/wiki/Battle_of_Vienna