The lower part (base/drums) of the Green Dome (Ghumbad‑e‑Masjid‑e‑Nabawi) is octagonal —it has 8 sides.

Why it’s 8-sided

-The Green Dome sits over the chamber that contains the tombs of the Prophet Muhammad ﷺ, Abu Bakr, and Umar. Historically and architecturally, that chamber and the dome’s supporting structure are described as having an octagonal base.

-This octagonal form is a common feature in Islamic monumental architecture for transitioning from a square or rectangular room below to a circular dome above, often using an eight-sided drum or zone of transition.

Context around the dome

-The dome itself is known as the Green Dome and is one of the most recognizable features of Al‑Masjid an‑Nabawi in Medina.

-The mosque has been expanded many times over the centuries, but the dome’s position above the sacred chamber has remained a focal point through all renovations.

TL;DR

The lower part of the Ghumbad‑e‑Masjid‑e‑Nabawi (Green Dome) has **8 sides** (it’s octagonal).[5] Information gathered from public forums or data available on the internet and portrayed here.