Piero della Francesca is known as an important Italian Renaissance painter. From his c. 1466 fresco cycle "The Legend of the True Cross", which includes this painting:
The Queen of Sheba in adoration of the Wood and the Meeting of Solomon and the Queen of Sheba, Gianoli has selected this detail:
The striking white horse must belong to the Queen of Sheba. And the black horse to the left is certainly communicating something to someone.
But the thing I find most charming is how the artist depicted the horse who is looking out at us over the white horse's saddle. I imagine this tells us something about della Francesca as a horseman as well as an artist.
NB: Wikipedia notes of Piero della Francesca, "As testified by Giorgio Vasari in his Lives of the Artists, to contemporaries he was also known as a mathematician and geometer."
Note: The book is: Horses and Horsemanship Through the Ages, by Luigi Gianoli, translated by Iris Brooks. First published in Italian as Il Cavallo e l'Uomo, 1967 by Longanesi and C. First published in the United States by Crown Publishers, Inc. 1969.