In 1981, "Defender" established scrolling in shoot 'em ups, offering horizontally extended levels. Unlike most later games in the genre, the player can move in either direction. The scrolling helped remove design limitations associated with the screen. Though the minimap had been used before (such as in 1980's "Rally-X"), "Defender" integrated it in a more essential manner. Konami's "Scramble", released in 1981, is a side-scrolling shooter with forced scrolling. It was the first scrolling shooter to offer multiple, distinct levels. Atari's "Tempest", released in 1981, is one of the earliest tube shooters and an early attempt to incorporate a 3D perspective into shooter games. "Tempest" ultimately went on to influence major rail shooters.