Polis horse

Gavinton is a sleepy village of maybe 200 people. Once a year the Reivers visit. Still don't know what it's all about but 60 horses and riders turned up with a pipe band and about 6 or 700 people appeared. A special song was sung, lots of booze and burgers and facepaint and balloon distorting - but why?
And of course the jolly polis saw me with my camera and one had to put his hat on a horse.
It was certainly the funniest thing that ever happened and will be talked about for generations.
The horse is Roger (I think) and is 17 and a quarter hands.