Although stealth gameplay had appeared in previous games, 1998 is seen as a turning point in gaming history because of the release of ', "Metal Gear Solid", and '. The ninja-themed "Tenchu: Stealth Assassins" was the first 3D stealth based-game. Months later, the highly anticipated "Metal Gear Solid" transformed its modestly successful franchise into a mainstream success. The increased power of the PlayStation console over previous platforms allowed for greater immersion in terms of both story and game environment. "Metal Gear Solid" has been credited with popularizing the stealth genre. "Thief: The Dark Project" is also credited as a pioneer of the genre. It was the first stealth game using the first-person perspective, dubbed a "first-person sneaker", or "sneak-em-up", and the first to use darkness and shadows as the mode of concealment. Another of Thief's most noteworthy contributions to the genre was the use of sound as a central mechanic. The robust simulation of sound meant players had to be mindful of the sounds they made, including what kind of surface they were traversing, lest they draw attention to them. Conversely, it meant guards could be heard from a distance and the surfaces they moved on could be identified based on the sounds they made.