Let’s begin by looking at the similarities between the architecture of Humayun’s Tomb and the Taj Mahal. Both have large, rectangular pistaq entrances, the tops of which break above the rest of the facade. They frame pointed-arch iwan niches. You can see this pistaq-iwan niche combination repeated on both facades. There’s a clear prototype for this arrangement in the earlier Timurid Madrasa of Ulegh Beg, which was built between 1417-1420 in Samarkand, Uzbekistan.
Additionally, both have large bulbous domes that rise above the tomb at the center, they feature Hindu-inspired chhatri pavilions and have chamfered corners that give the impression of depth. Finally, they sit on elevated platforms, symbolic of their importance.
This is where things get interesting! The Taj has Quranic inscriptions that communicate a clear narrative to the visitor. (In the video, we zoom in so we can see them more clearly.) They convey an apocalyptic message focused on judgement and the potential for salvation. Another difference is the color scheme: In Humayun’s Tomb, white marble is used exclusively to highlight key features, while at the Taj, the entire tomb is white. The facade of Humayun’s Tomb undulates, with octagonal wings that flank the entrance projecting forward. These projections are eliminated at the Taj. Finally, the dome changes form. You can see how the Taj’s dome is more elevated and significantly more bulbous.