Humayun's Garden Tomb is essentially a mausoleum that sits in a large garden with a charbagh plan.
A charbagh garden is a garden that is divided by two intersecting channels of water.1 Catherine Asher explains why Humayun's Garden Tomb is considered a charbagh garden and what this means.
Upon entering any gate, the centrally situated tomb and its charbagh setting are visible. Each of the four garden plots is further sub-divided by narrower waterways. Based on the charbagh types established in Iran and more fully developed in Babur's own concept of the ideal garden, such formalized and geometrically planned garden settings became standard for all the imperial Mughal mausoleum and for those of many nobles as well. charbagh gardens long had been associated with paradisaical imagery. But at Humayun's tomb, the association is all the more explicit, for the water channels appear to vanish beneath the actual mausoleum yet reappear in their same straight course on the opposite side. This evokes a Qur'anic verse which describes rivers flowing beneath gardens of paradise.2
1. Catherine B. Asher, Architecture of Mughal India (Cambridge: Cambridge University Press, 1992), xxv.
2. ibid, 45.
Asher, Catherine B. "Babur and the Timurid charbagh: Use and Meaning." Environmental Design 9, no. 1-2 (1991): 46-55.
Balasubramaniam, R. "On the Modular Design of Mughal Riverfront Funerary Gardens." Nexus Network Journal 12, (2010): 271-85.
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.
Ruggles, D. Fairchild. "Humayun’s Tomb and Garden: Typologies and Visual Order." In Gardens in the Time of the Great Muslim Empires, edited by Attioli Petruccioli, 173-86. Leiden: E.J. Brill, 1997.
—. Islamic Gardens and Ladnscapes. Philadelphia: The University of Pennsylvania Press, 2008. Chapter 4
Wescoat, J.L. Jr. "The Islamic Garden: Issues for Landscape Research." Environmental Design: Journal of the Islamic Environmental Design Research Centre 1, (1986): 10-19.
—. "Mughal Gardens: History, Geography, and Culture." In Heritage of the Mughal World, edited by Philip Jodidio, 97-111. Munich: Prestel, 2015.