The limestone White Chapel of king Senusret I was built for his Heb-Sed celebrations. The Heb-Sed, or the Sed festival, marking one of the most important event in the king's life, was celebratedafter the king has ruled for 30 years and was repeated every 3 years after that.
The purposes of the festival were to ritually rejuvenate the king's powers so that he can continue ruling effectively and to commemorate his ascension to the throne.
Its origins are very ancient. As it is celebrated after 30 years of rule, it is believed that originally when a rule's powers appeared to be fading due to his age, he was expected to run a race in front of his subjects to prove that he is still competent to rule.
The White Chapel of Senusret I is a building specially prepared for this occasion. The shrine has four interior pillars surrounded by a peristyle of twelve pillars. We do not know where in Karnak the chapel stood originally. However, due to the existence of a waterspout on one side, it has been suggested that it may have stood in the open air.
The building has been dedicated to Amun-Ra and the reliefs depict the king being crowned and embraced by Amun, Horus, Min and Ptah. The reliefs are one of the highest quality seen on ancient Egyptian monuments. Along the base of the outer walls we find reliefs depicting the emblems and deities of the nomes (provinces) of Egypt.
It is presumed that when in use during the Heb-Sed, a throne was placed in the middle where the king rested during the festival. This was later replaced by a bark repository where the procession carrying the sacred bark for ceremonies could halt.
Amenhotep III dismantled the White Chapel during his renovation of the area around the festival hall of Thutmose II and used it as fill in his newly constructed Pylon III. It has been discovered in 1927 by Henri Chevrier and all the pieces - more than 950 blocks - have been removed between 1927 and 1930. The pieces were then assembled into the building we can view today in the Karnak Open Air Museum.