S.A.A. Naqvi describes Humayun's Tomb's plinth in his book Humayun's Tomb and Adjacent Buildings.
In the centre of the garden the mausoleum itself rises from a wide and lofty platform 22 feet high, which in turn stands upon a podium 4 feet high. The latter is the only feature of the mausoleum built of quartzite, the remainder being entirely of red or yellowish sandstone with marble panels or outlines and a marble-covered dome. In each side of the high terrace are seventeen arches, while at each corner an oblique arch cuts the angle. The central arch on each side opens on to an ascending staircase. To the east of the southern stair a horizontal passage leads to the actual tomb below the monument. The remaining arches open into cells most of which contain subsequent burials. The floor of the terrace is paved with red sandstone and contains a number of unidentified graves.1
1. S.A.A. Naqvi, Humayun's Tomb and Adjacent Buildings (New Delhi: Archaeological Survey of India, 1947), 9-10.