These Three Grottoes were used as levels for the initiation of Daoist masters, from lowest to highest .
As well as the Three Grottoes there were Four Supplements that were added to the Canon circa C.E. 500. These were mainly taken from older core Daoist texts apart from one which was taken from an already established and separate philosophy known as Tianshi Dao .
Although the above can give the appearance that the Canon is highly organised this is far from the truth. Although the present-day Canon does preserve the core divisions there are substantial forks in the arrangement due to the later addition of commentaries, revelations and texts elaborating upon the core divisions.
#The First Daozang
#*This was the first time an attempt was made to bring together all the teachings and texts from across China and occurred circa C.E. 400 and consisted of roughly 1,200 scrolls
#The Second Daozang
#*In C.E. 748 the Tang emperor Tang Xuan-Zong , sent monks to collect further teachings to add to the Canon.
#The Third Daozang
#*Around C.E. 1016 of the Song dynasty, the Daozang was revised and many texts collected during the Tang dynasty were removed. This third Daozang consisted of approximately 4500 scrolls.
#The Fourth Daozang
#*In C.E. 1444 of the Ming dynasty, a final version was produced consisting of approximately 5300 scrolls.
Three Grottoes 三洞 C.E. 400
#Authenticity Grotto 洞真部: Texts of Supreme Purity tradition
#*This grotto is concerned mainly with meditation and is the highest phase of initiation for a Daoist master.
#Mystery Grotto 洞玄部: Texts of Sacred Treasure tradition
#*This grotto is concerned mainly with rituals and is the middle phase of initiation for a Daoist master.
#Spirit Grotto 洞神部: Texts of Three Sovereigns tradition
#*This grotto is concerned mainly with exorcisms and is the lowest phase of initiation for a Daoist master.
Each of the above Three Grottoes then has the following 12 chapters
#Main texts 本文類
#Diagrams and illustrations 靈圖類
#Histories and genealogies 譜錄類
Four Supplements C.E. 500
#Great Mystery 太玄部: Based on the Dao De Jing
#Great Peace 太平部: Based on the Taiping Jing
#Great Purity 太清部: Based on the Taiqing Jing and other texts
#Orthodox One 正一部: Based on the Way of the Celestial Masters tradition.