Thomas Walling drummed in Symphony X for a short while in 1999, temporarily replacing Jason Rullo.
After the critically acclaimed "The Divine Wings of Tragedy" Jason Rullo decided to leave the band. With Walling on drums Symphony X released "Twilight in Olympus" in 1998. This release garnered both greater critical kudos and greater sales.
However, newcomer Walling decided that he was not up to touring for the album. The departed Rullo rethought his exodus and came back into the Symphony X fold.