According to al-Sumaria news, they began the march in Ras al-Bisheh, a town in the southernmost part of the southern province of Basra, on Saturday.
Arbaeen, which is one of the largest religious gatherings in the world, comes 40 days after Ashura, the martyrdom anniversary of the third Shia Imam, Imam Hussein (AS).
Each year, a huge crowd of Shias flock to the Iraqi city of Karbala, where the holy shrine of Imam Hussein (AS) is located, to perform mourning rites.
Arbaeen falls on October 19 this year.