Our Prophet (saas) informed that at the Hazrat Mahdi (as) letter would be written on the pier of the bridge in Constantinople which is Istanbul

Ghaibat Nomani: It is narrated from Ahmad bin Hawza from Nahawandi from Abdullah bin Hammad Ansari from Muhammad bin Ja’far that Imam Sadiq (a.s.) said:

“When Qaim (a.s.) rises up… he would dispatch an army to Constantinople. When it reaches the gulf they would write something with their feet and walk on the surface of the water. The people of Constantinople will say: They are the companions of one who walks on water… At that moment they would open up the gates of the city for them.”