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The series incorporates themes from multiple genres, including fantasy fiction, science fantasy, horror and western elements. They describe a gunslinger's quest toward a tower whose nature the books call both physical and metaphorical.
In the story, Roland is the last living member of a knightly order known as gunslingers. The world he lives in is quite different from our own, yet it bears striking similarities to it. Politically organized along the lines of a feudal society, it shares technological and social characteristics with the American Old West, as well as bearing magical powers that are supposedly gone but there are some quantities hidden, and the relics of a highly advanced, but long vanished, society. Roland's quest is to find the Dark Tower, a fabled building said to be the nexus of all universes. Roland's world is said to have “moved on,” and indeed it appears to be coming apart at the seams — mighty nations have been torn apart by war, entire cities and regions vanish from the face of the earth without a trace, time does not flow in an orderly fashion; even the sun sometimes rises in the north and sets in the east. As the series opens, Roland's motives, goals, and his age are unclear, though later installments shed light on these mysteries.