The Devanāgarī alphabet has been shown by Bühler to have been -L derived from the Brahmī, in which the earliest documents and most of Asoka's inscriptions are written. With the revival of Sanskrit learning and literature, which took place in the fourth and fifth centuries A.D. under the Gupta emperors, the development of the Brahml script proceeded apace. The first step or innovation was the method adopted by which the letters were made to hang from the horizontal top-line. This line first appears to a marked degree in the period, dating from 350 after Christ, but becomes only fully developed in the scripts circa A.D. 800–1200. Thus the p of the Baijnāth Prasastī (A.D. 804) has an open top, but appears with a closed top, , in the Kanheri cave inscriptions, only to open out again in the tenth century. The character may be regarded as having become fixed in the eleventh century (vide Bhimadeva's script A.D. 1029). And similarly with other letters.