Muslims commemorate the fortieth day after the martyrdom of Imam Hussain (AS) and his companions, called Arbaeen, meaning the fortieth day in Arabic. They all gather around the city of Karbala and Imam Hussain’s (AS) shrine, mourning and lamenting the unfair and cruel war between his comrades and those of Yazid Ibn Muawiyah, which led into the death of those pure men and the bondage of their families. 

This commemoration happens every year around the city of Karbala. Muslims begin to walk to Karbala from other towns. They gather together in groups to pray, and especially to mourn the martyrdom of Imam Hussain (AS).
This walk is a hard one. It takes at least three days and lots of energy and time. So, why do Muslims take that? What is the philosophy behind it? 

To answer our questions, first, let’s have a review of the history behind this walk and then move to the other aspects of this commemoration. 

1. What is the Arbaeen Walk?

The history of Arbaeen walk goes back to the first visitors of Imam Hussain (AS) after his death. On the day of Arbaeen, forty days after the tragic martyrdom of Imam Hussain (AS), Imam’s (AS) son, sister and the remaining members of his family and that of the other martyrs came back to Karbala to lament the death of their dear ones besides their graves.  

Their next visitor was Jabir Ibn Abdullah Ansari on the year 61 AH. Visiting Imam Hussain’s (AS) shrine was a tradition in Shiite culture until a short period after Morteza Anasari’s became the religious reference (Marja’) of Shiite Muslims. It was then lessened for some years and then revived. Some other religious references (Marja’) kept this tradition alive among their followers, until the government of Saddam Hussain, which banned all religious Shiite traditions to be performed publically [1]. 

The tradition was revived after the fall of Saddam, and it is still to be continued. 

2. Why on Foot?

Visiting the holy shrines and going on pilgrimages on foot is not something new or belonging to our age. It’s got a long history, and Adam did the first pilgrimage on his visit to Mecca [2]. It isn’t a tradition just among Muslims either. It is performed in other faiths and religions, too. For instance, Caesar made a vow to his God to go on a pilgrimage to the Dome of Rocks if he won the battle against the Empire of Persepolis (Iran). He performed his vow after his victory [3].

Pilgrimages are highly admired, and their act is seen as a way of getting closer to Allah by Imam Sadiq (AS). Visiting the holy shrines of the twelve Imams (AS) is even more praised, especially the sacred shrine of Imam Hussain (AS). Of course, it’s not these shrines themselves that are of value and importance, but the people who have been buried there. Thus, when one makes a pilgrimage toward these shrines, he/she finds the chance to think more about these great personalities who won Allah’s satisfaction and praise and were Muslims in the real sense of the word. So, in every step that a pilgrimage takes toward Imams' (AS) shrines, especially that of Imam Hussain (AS), he/she is getting closer to a source of spiritual blessing, bringing him/her thousands of virtues and wiping away thousands of vices from his/her mind and soul.

3. What is the Philosophy behind the Arbaeen Walk?

The Arbaeen pilgrimage is not merely a long walk. Instead, it is a kind of movement in which despite being in publics, pilgrims have their own private relationship with Allah and Imam Hussain (AS), which finds a new form of divine immaterial dependence and conformance. Thinking about the goals and the history behind the martyrdom of Imam Hussain (AS), the injustice and cruelty imposed on his family and the devotions of his faithful followers brings about many personal and social growth and improvements. 

Meeting other Muslims, exchanging ideas, and making friendships with Muslims of the other countries is another social outcome of this pilgrimage. One finds out that they are not alone in their faith, and have friends all over the world. They may have differences, but they have one thing in common: Belief in Imam Hussain (AS) and his right cause. 

The last and the most crucial point to mention this great gathering is it's a kind of preparation for the grand reappearance of Imam Mahdi (AS), the awaited savior among Muslims. The Arbaeen pilgrimage is to make the minds and souls ready for this great event. It is said that when Imam Mahdi (AS) reappears, he introduces himself as the son of Hussain (AS) [6], whose fame has reached many people through the Arbaeen Pilgrimage; one of the most significant religious gathering around the world, with the estimated number of 40,000,000 people participating in it, whose news is broadcasted all over the world [5].  

References

1. "The background of Arba'een rally/The importance of Najaf-Karbala rally from the scholar's viewpoint." Fars News. Archived from the original on 16 November 2015. Retrieved 4 October 2015.
2. Hor Ameli, Muhammad Bin Hussain Vasayel-o-Shia, Vol 11, p 132
3. Sobhani, Jafar The Light of Eternity p. 696
4. Kamel-o-Ziyarat: Pp 183, 184 and 185
5. Philipson, Alice (19 January 2015). "The ten largest gatherings in human history." The Telegraph. Archived from the original on 6 October 2015. Retrieved 3 October 2015. 
6. Khademi Shirazi, Mohammad Yad’e Mahdi P16, P132

Every age has its defining genius, every culture its own Aristotle, Leonardo or Goethe. For classical Islam, one of those figures is unquestionably Ibn Sina or Avicenna (his Latinized name). A marvelous man by whose eighteenth birthday his fame as a physician was so great that he was summoned to treat the dying Samanid king of Bukhara (976-97 A.C) when all the talented court physicians had given up hope of his recovery. To the great astonishment of all, he was given the privilege of using the court's remarkable library which was the highest award for his future successes.

It is hard to describe Avicenna in any word but superlative. He wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived. His intellectual achievements encompassed not only medicine, but philosophy, law, science, music, poetry, mathematics, and statecraft. Even his life was the stuff of legends.

The only source of information for the first part of Avicenna's life is his autobiography, as written down by his student Juzjani. Now let's have a glimpse at his life in his own words:

“My father Abdullah was from Bukhara. Bukhara at that time was one of the greatest cities in Persia. He was appointed as a Samanid governor married to my mother Setareh, and I was born there in 980 A.D. They called me Hussain, some years later my father was posted to Bukhara, where I received my early education in literature and Quran. From the very beginning I made such remarkable progress in my education that at the age of 10, I had completely memorized the Quran. Abu Abdullah al Natili, a leading philosopher of his time, visited Bukhara and stayed at our home. I learned logic, geometry, and astronomy from him. I soon surpassed my teacher and studied medicine, physics, and metaphysics by myself and mastered all these subjects before I was 17 years old. Then, I started writing at the age of 21”.

Ibn Sina's chief work is the monumental "Al-Qanun," which is over one million words in length, in medicine. The instructions of this book were Europe's pharmacopeia for five centuries after his death.  Al-Qanun discusses the whole field of medicine in an attempt to codify all the existing medical knowledge.

Another important work, a commentary on the work of Aristotle, was designed to set out the philosophies of ancient Greeks. Al Kitab ash-Shifa (the book of healing) is the most extended treatise on philosophy ever written by a single man.

In the end, the repeated travels and exacting political and intellectual preoccupations of Ibn Sina deteriorated his health. He was suffering from colic, and he made some extraordinary efforts towards his treatment.

He became bedridden in Hamadan (Iran), and died at the age of 57 in 1037 A.D., being the victim of a disease in which he was a specialist. His grave in Hamadan is yearly visited by a large number of admirers.

As one of the historians said, Avicenna is like a meteor, which flashed across the sky, illuminating the whole world with his brilliance, and in whose afterglow we still perceive the world around us.

References:

1.  Avicenna