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 combination is called 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 gains the ability to hold a pointed bulbous form that wouldn't otherwise be possible.
1. Ali Tavakoli Dinani, Solmaz Sadeghi, and Paulo B. Lourenço, "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. Rafael. Aguilar et al. RILEM (Cham: Springer Nature Switzerland, 2019), 90.
Golombek, Lisa, and Ebba Koch. "The Mughals, Uzbeks, and the Timurid Legacy." In From the Mongols to Modernism, edited by Finbarr Barry Flood and Gülru Necipoglu, 811-45. Vol. 2 of A Companion to Islamic Art and Architecture. Oxford: Wiley Blackwell, 2017.
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 H. Boeschoten and M. Van Damme, 255-86. Utrect: Institute of Oriental Languages, University of Utrecht, 1987.
Dinani, Ali Tavakoli, Solmaz Sadeghi, and Paulo B. Lourenço. "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 Rafael Aguilar et al., 87-95. RILEM. Cham: Springer Nature Switzerland, 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." In Proceedings of the First International Congress on Construction History, Madrid, 20th-24th January 2003, edited by S. Huesta, 1941-52. Madrid: I. Juan de Herrera, SEdHC, ETSAM, A.E. Benvenuto, COAM, F. Dragados, 2003.
Nizamuddin Urban Renewal Initiative. "Restoring the Marble Dome 2009-11."