The importance of Constantinople is self-evident, as it not only connects the European and Asian parts of the Ottoman Turkish Empire, but also controls the connection between the Black Sea and the Mediterranean Sea.
Outside of Constantinople, the Turkish Empire established a heavily fortified military town to protect its capital.
Adriafort, one of the strongest military fortresses in the European part of the Turkish Empire, is second only to the impregnable capital city of Constantinople.
After the war broke out, the Turkish government specifically withdrew some of the troops from Albania and Macedonia to garrison Adriafort, located in the Sevres area.
This is the outpost for Bulgaria and Balkan nations on the way to Constantinople, as well as the last line of defense for the capital of the Ottoman Turkish Empire.
If Adriafort falls, Sevres will be a smooth path, and the enemy's army will quickly arrive at Constantinople.