Christ Giving the Keys to St. Peter, 1481 Fresco. 11' 5 1/2" x 18' 8 1/2 ". Sistine Chapel, Vatican, Rome- by Perugino
"d" points out the orthogonals.
Orthogonals: Lines running at right angles to the plane of the picture surface but, in a representation using one-point perspective, converging toward a common vanishing point in the distance. (Hart)
The lines on the ground in the middle ground of Perugino's fresco are a nice example of orthogonals.
Paolo Uccello loved the use of orthogonals, some say he 'overdid' his use of them in most of his paintings - The Battle of San Romano is a nice example - especially in the foreground.