A dome's drum is an architectural element that is used to lift the dome higher. The dome's drum and the massive white marble dome hoist the shahada finial up above Humayun's Tomb's pishtaqs and proclaims that Allah is the one and only god.
The dome's drum has eight evenly spaced passageways for accessing the roof terrace. There is a large waterspout above the western passageway and the eastern passageway to redirect water when it rains.
The dome's cylindrical drum has three horizontal layers. Taking up the bottom two thirds of the drum, the base layer is surfaced with a polychromatic 6-pointed stellate lotus pattern that is articulated with coursing and bonding using two different colors of sandstone. Each shape in this pattern is embedded with a dark gray shale stylized flower symbol. The top layer of the dome's drum is a ring of dark brown stone muqarnas that appears like a ring of tiny corbel brackets set side by side to support a gigantic dome. A ring of white marble dressing with red sandstone trim divides the muqarnas layer from the base layer. Each layer is very different from the other, but they stack up into a single consistent transitional form to support the massive marble dome.
Lowry, Glenn. "Humayun's Tomb: Form, Function and Meaning in Early Mughal Architecture." Muqarnas 4, (1987): 133-48.
Michell, George. The Hindu Temple: An Introduction to its Meaning and Forms. Chicago: The University of Chicago Press, 1988, 78-85.