With Planescape, we have an attempt by an AD&D game setting to add layers of intellectual complexity to a game often driven by much more simplistic mechanism. The greatest commerce isn't loot, treasure, magic items, etc.; it is belief so strong it can shape reality". In a review of The Great Modron March, Backstab magazine contributor Philippe Tessier called the presentation of Planescape products superb in general. Cosmology The Dungeons & Dragons cosmology as reflected in Planescape consists of a number of planes, which can be divided into the following regions: The Inner Planes (representing planes of elemental nature, such as Water, Earth, Fire, and Air, as well as the Positive and Negative energy planes) The Ethereal Plane The Prime Material Plane The Astral Plane The Outer Planes (representing alignments and the primary domains of the various deities, where their petitioners spend their afterlives) Planescape "solidified the Great Wheel cosmology that began in 1e and would later be reinstated in 5e as the dominant of three theoretical models". Outer Planes The Outer Planes consist of: the Abyss, Acheron, Arborea, Arcadia, Baator, Beastlands, Bytopia, Carceri, Elysium, Gehenna, Gray Waste of Hades, Limbo, Mechanus, Mount Celestia, the Outlands, Pandemonium, and Ysgard. Sigil Sigil, the "City of Doors", is located atop the Spire in the Outlands. It has the shape of a torus, and the city itself is located on the inner surface of the ring. There is no sky, simply an all-pervasive light that waxes and wanes to create day and night. Sigil cannot be entered or exited save via portals. Although this makes it quite safe from any would-be invader, it also makes it a prison of sorts for those not possessing a portal key. Thus, many call Sigil "The Bird Cage" or "The Cage." Though Sigil is commonly held to be located "at the center of the planes" (where it is positioned atop the infinitely tall Spire), some argue that this is impossible since the planes are infinite in all dimensions, and therefore there can never truly be a center to any or all of them. Curiously, from the Outlands, one can see Sigil atop the supposedly infinite Spire. Factions Within Sigil there are philosophy-derived factions. Before the event known as the Faction War, the groups controlled the political climate of Sigil. Each of these factions is based on one particular belief system; one faction's beliefs make them enemies while