There is an architectural reason why a dome applied in a mosque/masjid: so that a mosque/masjid does not require lot of pillars or shaft. Without pillars, people can make rows without space (for pillar or shaft) when makes sholat/pray.
Answer 1
It is just a traditional mosque architect art. It is not an Islamic religion requirement.
Answer 2
The dome shape was copied from pre-Muslim Byzantine architecture. Lots of the Muslim Koran is copied from the Old Testament, so it seems the Muslims couldn't think of anything new in building design either. Domes feature in even earlier Roman buildings too. The inside of a dome always strikes me as more interesting than the outside, because you can see the structure and it`s often decorated. To early Christians - and Muslims - the inside of the dome probably reminded them of Heaven, because the writers of The Bible and later Koran thought the earth was flat and that Heaven was suspended or supported above it like an upside-down saucer.
It is more incidental than actually religiously mandated. When the Muslims were exclusively in Arabia, most of their mosques were boxy-structures. This remains the general shape of the Masjid al-Haraam (Great Mosque in Mecca) and the Masjid an-Nabawi (Prophet's Mosque in Medina). When the Muslims conquered Egypt and the Levant they took over Byzantine territory with a number of Byzantine churches. It was typical of Byzantine Church architecture to have domes in their churches.
As more and more former Byzantine Christians converted to Islam, churches were converted into mosques and the domes survived. The Muslims began to identify with the Byzantine dome-structure since there were more Byzantine Churches that were converted into Mosques than typical Arabian Mosques. So, the dome became an iconic symbol of a mosque.
Some of the earliest mosques were Orthodox churches commandeered by the conquering Muslim forces. Orthodox churches had domes, and often still do, so the Muslims adopted the architecture as their own. Orthodox Christians had used domes because they allowed the largest possible uninterrupted floor space without pillars.
Culture. Not all mosques have domes on top, such as Chinese mosques and African mosques.
Another answer from our community:
It may have Acoustic advantage to amplify the voice during prayers
It is just an architect that characterises the mosque for Muslims. It is not obligatory or mandatory for mosque to be designed with a dome.
well it is for sumin like the sun
The roof of a mosque is generally in the shape of a qubah or dome, depending on the size of the mosque. Bigger mosques may have several dome-shaped roofs plus flat roofs for the rest of the prayer hall.
As much as I know, it is the mosque that Isa ( alahissalam) will descend ( on the roof of) before Day of judgement!!!
Because the dome is the holy thing in the mosque. A dome is placed inside a mosque to allow the air to circulate around the mosque.
It is an Islamic architect
Concave roof is a roof in the form of a dome or circular shape. A concave roof is one which slopes downward toward the center. You can remember this by thinking the roof is "cave"-ing in.
Painting the dome with gold is not necessary.
Dome
A rounded roof built on a circular base is a dome.
It is a mosque, built on the Jewish Temple Mount.
Byzantine culture influenced a lot of Islamic architecture especially the dome shape that many Mosque have.
Dome Dome
a minaret