What happened at Karbala did not remain an event. It became a form of worship, and the transformation is one of the most complete examples in any religion of a historical episode turned into an annual re-entry.
The first ten days of Muharram are given to mourning assemblies in which the narrative is recited and the congregation weeps. Elegiac poetry in Arabic, Persian, Urdu and other languages forms a literature of its own. Processions carry replicas of the shrine and banners of Abbas. In Iran the taziyeh developed as a passion play, one of the few dramatic traditions in the Islamic world. Practices of self-mortification exist and are contested within the community, with senior jurists on both sides of the question.
Forty days later, Arbaeen draws millions on foot to Karbala, among the largest annual gatherings of people anywhere on earth, with food and shelter provided free along the roads by households and volunteers.
The meaning attached to the event is not primarily historical but moral: righteous suffering under unjust power, the refusal to give allegiance to a ruler judged illegitimate, and the obligation to remember what one failed to prevent. Karbala functions in Shia thought as a permanent measure of political conduct, and the phrase that every day is Ashura and every land is Karbala is the standard expression of it.