[The Might]

Actually, I have always seen Vienna as Minas Tirith.
For the Turks it was the key to gain passage into western Europe, just as Minas Tirith was the key city that Sauron needed to destroy. Both cities were in bad condition when reinforcements arrived. Both times reinforcements were cavalry (Rohirrim / Polish hussars).
Also, the main difference is that Vienna just like MT withstood the assault, while Constantinople did not.