TEHRAN(Basirat):The Arba'een Pilgrimage is the world's largest public gathering that is held every year in Karbala, Iraq. This Ziyarah (pilgrimage) is held at the end of the 40-day mourning period following Ashura. Shia Muslims of Nigeria in west of Africa take themselves to Karbala in spite of it is very far for them.

Why do 20 million humans from all around the globe gather on the land of Karbala, Iraq?