The site was originally Muhammad (P.B.U.H)'s house; he settled there after his Hijra (emigration) to Medina, later building a mosque on the grounds. He himself shared in the heavy work of construction. The original mosque was an open-air building. The basic plan of the building has been adopted in the building of other mosques throughout the world.
The mosque also served as a community center, a court, and a religious school. There was a raised platform for the people who taught the Quran.
The original mosque was built by Hazrat Muhammad(P.B.U.H) next to the house where he settled after his journey to Medina in 622 AD. The original mosque was an open-air building with a raised platform for the reading of the Quran. It was a rectangular enclosure of 30 × 35 m (98 × 115 ft), built with palm trunks and mud walls, and accessed through three doors: Bab Rahmah (Door of Mercy) to the south, Bab Jibril (Door of Gabriel) to the west and Bab al-Nisa' (Door of the Women) to the east.
The latest renovations took place under King Fahd and have greatly increased the size of the mosque, allowing it to hold a large number of worshippers and pilgrims and adding modern comforts like air conditioning. He also installed twenty seven moving domes at the roof of Masjid Nabawi.
The mosque has a flat paved roof topped with 27 domes on square bases. Holes pierced into the base of each dome illuminate the interior. The roof is also used for prayer during peak times, when the domes slide out on metal tracks to shade areas of the roof, creating light wells for the prayer hall. At these times, the courtyard of the Ottoman mosque is also shaded with umbrellas affixed to freestanding columns. The roof is accessed by stairs and escalators. The paved area around the mosque is also used for prayer, equipped with umbrella tents.The north facade has three evenly spaced porticos, while the east, west and south facades have two. The walls are composed of a series of windows topped by pointed arches with black and white voussoirs. There are six peripheral minarets attached to the new extension, and four others frame the Ottoman structure. The mosque is lavishly decorated with polychrome marble and stones. The columns are of white marble with brass capitals supporting slightly pointed arches, built of black and white stones. The column pedestals have ventilation grills that regulate the temperature inside the prayer hall.
This new mosque contains the older mosque within it. The two sections can be easily distinguished: the older section has many colorful decorations and numerous small pillars; the new section is in gleaming white marble and is completely air-conditioned.The open courtyard of the mosque can be shaded by folded, umbrella-like canopies.
The heart of the mosque houses a very special but small area named ar-Riaz-ul-Jannah, which extends from Hazrat Muhammad(P.B.U.H.)'s tomb (Rawda) to his pulpit. Pilgrims attempt to visit and pray in Riaz-ul-Jannah, for there is a tradition that supplications and prayers uttered here are never rejected.
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