However Lewis, 30, will now link up with fellow former Wales forwards Jon Humphreys and Christian Loader when he joins Bath, who will compete in the Heineken Cup this season.
'I'm pretty lucky because the timing was not great for me to find a new club and Bath is still such a big name,' he said.
'It was very disappointing that things did not work out well for Rotherham and it's really a miracle that they survived.
'But this is a great opportunity for me. I know a few of the guys there already but no one needed to ask me twice about joining Bath - their reputation speaks for itself.
'When I first began playing rugby, Bath was the biggest name in English rugby and they are obviously striving to get back to those heights. It's just fortunate for me that they were on the look-out for a back-row.'
Bath Rugby became European champions when they beat Brive 19-18 in the 1998 Heineken Cup final.
This season, Bath are pooled with Leinster, Benetton Treviso and Bourgoin. They begin their campaign against Bourgoin on Saturday, October 23. (kick-off 14:15).