to troop the colours

from The Collaborative International Dictionary of English v.0.48

Troop \Troop\, v. t.

   {To troop the colors} or {To troop the colours} (Mil.),
   in the British army, to perform a ceremony consisting
   essentially in carrying the colors, accompanied by the band
   and escort, slowly before the troops drawn up in single file
   and usually in a hollow square, as in London on the
   sovereign's birthday.
   [Webster 1913 Suppl.]