Ar tonelico takes place in the world of Sol Ciel (ソル・シエール), which literally translates to "Sun Sky" in Latin and French, respectively, but means "Shining Sky/World" in the game's own language. The world consists of the living Tower of Ar tonelico and the Wings of Horus, a landmass connected to the lower portion of the Tower. Each section of the world above and below The Wings of Horus is designated with a specific name. The lower world is known for its small towns and is not considered to be very technologically advanced. The upper world is very advanced, and the Floating City of Platina is even considered to be a holy sanctuary by the Church of Elemia from the lower world. The Tower exists at the center of the world and is made from technology that was available prior to the world-destroying catastrophe known as the Grathnode Inferia. There is little land left after the two catastrophes of the past, so people have become increasingly dependent on Ar tonelico. The Tower functions much like a computer program, and is susceptible to viruses which are emerging at an alarming rate to wreak havoc on both the upper and lower worlds. Players may explore dungeons and other areas by moving in any direction and jumping. Depending on the abilities of the Reyvateils in the party, various spells can also be cast to light candles, remove obstacles, and trigger switches. Enemy creatures may be encountered at random as the player explores an area. A gauge in the lower-right corner of the screen indicates the likelihood of encountering an enemy, as well as the number of random encounters remaining in the current area. Ar tonelico features a turn-based battle system akin to those of the Atelier Iris series. The active party consists of up to three fighters in the front and one Reyvateil in the back. An action can be chosen for each fighter as their turn arrives. An action bar at the top of the screen indicates the turn order for every character and opponent involved in the battle. Fighters may choose to strike the enemy, defend themselves, use a skill, use an item, or to protect the Reyvateil.