The world's first "4D" roller coaster was X, which opened at Six Flags Magic Mountain in Valencia, California, on January 12, 2002. Designed by the now-defunct company Arrow Dynamics, the "4D" designation refers to the ride's unique ability to rotate the seats 360 degrees independently of the track's orientation. Unlike a standard coaster where you simply follow the path of the rails, X featured a "four-rail" system: two rails for the wheels to travel on, and two additional "gear" rails that controlled the seat rotation. This allowed the ride to flip passengers forward and backward in a synchronized "show" while plummeting down a 215-foot drop at 76 miles per hour. Due to its extreme complexity and heavy ride vehicles, the coaster suffered from frequent mechanical issues and a "bumpy" ride experience. In 2008, the ride underwent a massive $10 million renovation, which included lighter trains and the addition of fire and sound effects, and it was officially rebranded as X2. While other 4D coasters like Eejanaika in Japan have since been built, X remains the pioneer that introduced a completely new dimension of thrills to the amusement park industry.