The world of the marthiya opens with the constrained journey of the Imam Husayn and his relatives from Madina to Mecca. It extends along the Imam Husayn's journey from Mecca towards Kufa, which is intercepted at Karbala'. Karbala’ is the centre of this world, where the battle of truth is fought: the field of Destiny. From Karbala' it follows the caravan of the surviving widows and orphans and the sole surviving son of the Imam Husayn, the Imam Zayn al-Abidin, all chained and manacled, through the merry market crowds and festive courts of Kufa and Damascus.
The last phase is the return of this torn and tattered caravan from Damascus to Karbala', now turned into a graveyard, and from there back to Medina. At this point the world of marthiyacloses. It stretches like a track of light, a trail of suffering in the midst of deepening shadows of ghoulish darkness closing in upon it from all sides and trying to obliterate it. And yet this world, so narrow and confined in its temporal dimensions, is so immense in its relationships and significance. It reaches back to the days of the Holy Prophet and beyond it to the Divine Covenant on which the fate and future of Islam depends, and looks forward to the end of time and the Day of Judgement and Redemption. All nature and all history is deeply involved in the final outcome of these events and in what happens in this world. For the poet this world is inexhaustible, peopled with innumerable marthayas waiting for his eye and pen to be quickened into life.
source : http://www.al-islam.org