Humayun's Tomb actually has two domes. The massive white marble dome that Humayun's Tomb is known for is built on top of the dome that is visible as the ceiling of the cenotaph chamber. This is a double dome. "The integration of drum into the inner dome creates an optimized form in order to absorb the horizontal thrust. Consequently, the outer dome becomes more stable against lateral forces when compared to a single tall drum."1 As a result of this the dome is able to achieve greater height and the ability to support forms that wouldn't otherwise be possible.
1. Paulo B. Lourenco, Ali Tavakoli Dinani, and Solmaz Sadeghi, "A Double Dome Through the Ages: Building Technology and Performance of Esfahan Shah Mosque’s Dome," in Structural Analysis of Historical Constructions: An Interdisciplinary Approach, ed. R. Aguilar et al. (Cham, Switzerland: Spring, 2019), 89-90.
Hillenbrand, Robert. "Aspects of Timurid Architecture in Central Asia." In Utrecht Papers on Central Asia: Proceedings of the First European Seminar of Central Asian Studies held at Utrecht, 16-18 December 1985, edited by M. Van Damme and H. Boeschoten, 255-86. Utrect: Institute of Oriental Languages, University of Utrecht, 1987.
Lourenco, Paulo B., Ali Tavakoli Dinani, and Solmaz Sadeghi. "A Double Dome Through the Ages: Building Technology and Performance of Esfahan Shah Mosque’s Dome." In Structural Analysis of Historical Constructions: An Interdisciplinary Approach, edited by R. Aguilar et al., 87-95. Cham, Switzerland: Springer, 2019.
Parodi, Laura E. "The Posthumous Portrait of ‘Hadrat Jannat Ashiyani’: Dynastic, Saintly, and Literary Imagery in the Tomb of Humayun." Islamic Art 6, (2009): 129-58.
Tappin, Stuart. "The Structural Development of Masonry Domes in India"