When it came—and it's been a long time approaching—Valentino Garavani waved his last goodbye in a room literally lined with the ultimate image of his contribution to fashion: the gorgeous red gowns he has worked from first to last. It was just one red gown, actually—projected on the walls and worn by all of the models who filed out moments before Mr. Valentino took his final walk down the runway to a standing ovation. Uma Thurman was there to salute him, along with Lucy Liu, Alber Elbaz, Miuccia Prada, Nadja Auermann, Eva Herzigova, and Claudia Schiffer.