Ar tonelico
The First Tower of "Ar tonelico" is an "amplification Tower" that "supplies the people with an amplified version of the power of sounds on which Sound Science is grounded". While in the current times it has become a piece of lost technology, it still sees ample use due to its function as a "Song Magic Server", which makes it the power source for the Song Magic of the Reyvateils. Therefore, the Reyvateils in Sol Ciel all use the First Tower of Ar tonelico as their Song Server.