This article examines the architectural form and potential functions of two royal buildings: the Sher Mandal and the Guldasta pavilion. An octagonal tower located in the Purana Qilʿa in Delhi, the Sher Mandal was in all likelihood the library (kitāb-khāna) built by the Mughal emperor Humayun (r. 1530–56). Erected during the reign of the Safavid ruler Shah ʿAbbas I (r. 1587–1629), the now-vanished Guldasta pavilion was located south of the palace complex in Isfahan and can be studied through drawings and photographs. A close examination of the formal structure of the two buildings reveals that they belong to a distinct type of polygonal pavilion that first emerged in the late fifteenth century in the works of architecture sponsored by the Timurid dynasty (c. 1370–1405). Moreover, this comparative study opens up new venues for investigating the physical setting of the royal kitāb-khānain Mughal and Safavid contexts.