Where in the World: No.7

A Byzantine marvel
where spires pierce the sky,
This famous church is
a feast for the eye.
For centuries it has represented
it’s cities power and wealth
With tales it contains relics
of it’s patron Saint stolen in stealth.

Where in the world is this and what’s it’s name?

Note: Once someone has guessed the correct answer (here in a comment, or on Facebook, Twitter or Instagram), I’ll post the answer in the comments below and add the correct location on the map. Good Luck!