Hi Luigi!
While it is true that mountains are used symbolically to represent governments/kingdoms, in this case the seven heads of the dragon represent seven literal hills. We know this because the angel tells John "The woman you saw is that great city that rules over the kings of the earth." It also says that this woman who is a city, also sits on those seven literal hills, which is referring to her headquarters. Since the woman is said to be a city that sits on seven hills, then those seven heads cannot represent nations. The use of Symbolism represents the literal. In this case, the seven heads are symbolically representing seven literal hills.
While it is true that mountains are used symbolically to represent governments/kingdoms, in this case the seven heads of the dragon represent seven literal hills. We know this because the angel tells John "The woman you saw is that great city that rules over the kings of the earth." It also says that this woman who is a city, also sits on those seven literal hills, which is referring to her headquarters. Since the woman is said to be a city that sits on seven hills, then those seven heads cannot represent nations. The use of Symbolism represents the literal. In this case, the seven heads are symbolically representing seven literal hills.
Revelation 18:24 And in her was found the blood of prophets, and of saints, and of all that were slain upon the earth.