"We are judged all the way, from the moment we line up.
"They have to make sure they are all in the right place - they have to be two paces apart width ways and also stay in line, so there is a lot going on for them.
"They have to read music, walk and stay in time all together."
He said bands were also judged on how well they made turns.
Mr Thomas was from the Tauranga City Brass Band but was playing with the Rotorua band to bolster numbers, he said.
Rotorua businessman Tamati Coffey said there was a strong public turn out for the event.
He was supporting his partner Tim, a euphonium player in the Rotorua Brass Band.
"People have definitely showed up but in other cities they usually march through the middle of town so you get people who wouldn't normally see this stuff, or people who are in shops come out to watch, so we are playing to the converted."
Rotorua Brass Band E flat bass player Stephen Webb said it was a bit tricky to walk at the same time as play a brass instrument.