Evans, 29, joins compatriots and former Lions Ryan Jones and Dwayne Peel in the West Country and Holley admits he can't wait to see what his latest signing can do.
"These sort of fellas don't grow on trees. He's a physical specimen," said Holley.
"Worcester, our rivals in the Championship, were in for him as well. That shows the quality of the player.
"We're building a strong squad, combining a core of young Bristol players with some experienced internationals. And they want to be part of something special."