Translate the following English sentence to French:
"Twenty-one years later I have to tell you that yesterday evening in the forecourt in front of the Tower building, where the motorcyclists were collecting, there were sixteen flags flying."
Vingt-et-un ans plus tard, je dois vous dire qu'hier soir, dans l'avant-cour du Bâtiment Tour, où les motocyclistes se rassemblaient, il y avait seize drapeaux qui flottaient.