How much do you guys know about thresholds in traditional architecture?

Thresholds commonly have three kinds, one is directly fixed in the door pillow stone in the groove, the height is small, you can step across; one is movable, when needed, inserted in the door pillow stone in the wooden groove or bolts in the two door pillow stone between the height of about two feet; there is also a threshold (variations) is a pair of large doors can be free to open and close the door, basically in the height of more than three feet, and some even up to Six or seven feet in height, there will be a small door in the small door of two or three inches high wooden or stone small threshold.