The historian Ibn Kuluwayh mentioned that those who buried Imam Husayn [a], made a special and rigid construction with signs above the grave.
Higher and bigger constructions above the grave started during the ruling of Al-Saffah, but Harun al-Rashid later on, put heavy restrictions to prevent people from visiting the grave.
At the time of Al-Mamun, construction around the grave resumed until the year 236 AH when Al-Mutawakkil ordered the destruction and digging of the grave, and then filling the pit with water. His son, who succeeded him, allowed people to visit the grave site, and since then building the precinct to the grave increased and developed step by step.
On the other hand, the historian Ibn Al-Athir, stated that in the year 371 AH, Aadod Al-Dawla Al-Boowayhi became the first to largely lay the foundations for large scale construction, and generously decorated the place. He also built houses and markets around the precinct, and surrounded Karbala with a high boundary wall turning it into a strong castle.
In the year 407 AH, the precinct caught fire due to the dropping of two large candles on the wooden decorations, but Hasan ibn Fadl (the state minister) rebuilt the damaged sections.
History has recorded the names of several rulers who shared the honour of widening, decorating or keeping the precinct in good condition. Amongst them is Fateh Ali al-Qajari, who in 1250 AH ordered the construction of two domes. One over Imam Husayn's [a] grave and the other over his brother Abu al-Fadl Abbas [a].
The first dome is 27 meters high and completely covered with gold. At the bottom, it is surrounded with 12 windows, each of which is about 1.25 m away from the other, from the inside, and 1.30 m from the outside.
The mausoleum has an area of 59 m / 75 m with ten gates, and about 65 rooms (I wans), well decorated from the inside and outside, used as classrooms for studying.
As for the grave itself, in the middle of the precinct, it is called the "Rawda" or garden and it has several doors. The most famous one is called "Al-Qibla" or "Bab al-Dhahab". When it is entered, one can see the tomb of Habib ibn Madhahir al-Asadi, to the right hand side. Habib was a friend and companion of Imam Husayn [a] since their childhood. He was one of those who was honoured with martrdom at the Battle of Karbala.
source : http://www.al-islam.org
