In 1563, in Florence' s Palazzo Vecchio, Giorgio Vasari built in front of an existing wall a new wall on which he painted a mural  Investigators recently discovered a gap between Vasari' s wall and the original, large enough to have preserved anything painted on the original  Historians believe that Leonardo da Vinci had painted, but left unfinished, a mural on the original wall; some historians had also believed that by 1563 the mural had been destroyed  However, it is known that in the late 1560s, when renovating another building, Santa MariaNovella, Vasari built a facade over its frescoes, and the frescoes were thereby preserved
Thus, Leonardo' s Palazzo Vecchio mural probably still exists behind Vasari' s wall
When Vasari preserved the frescoes of Santa Maria Novella he did so secretly.