How Renaissance artists used science and math to more accurately mimic reality
Until Masaccio's Trinità fresco in Santa Maria Novella, painting had frequently used foreshortening to show depth, taking lines that in real life would be parallel (say, the top and bottom of a wall) and painting them instead to appear as if they were converging as they "receded."
This gave a decent illusion of distance and three-dimensionality, but until Masaccio, foreshortening was always done a bit haphazardly, with the artists merely eyeballing things and painting each instance of foreshortening according to its own internal logic.
Most artists of the early Renaissance era were constantly striving to add more naturalism to their work, and Masaccio provided them with the key. In the Trinità, all of the foreshortening lines are drawn to converge at to a single vanishing point at the back of the painted "vault" which contains the scene.
These days, kids get taught that in sixth grade art class, but at the time it was revolutionary. Renaissance artists flocked to study the new technique and apply it to make their scenes ever more realistic. Some, however, did an early Picasso and mastered perspective only to warp it as a storytelling, as did Paolo Uccello in the greenish frescoes of Noah in the adjacent cloisters.
The impulse to paint ever-more naturalistically dogged art for centuries, through the baroque, Neoclassical, and Romantic movements and right up to the photorealists of the 20th century. Interestingly, it wasn't until when photography came along that artists felt truly free from having to strive to record reality flawlessly.
This opened up new opportunities for Impressionists, Expressionists, and abstract artists. Some even turned perspective on its head. Picasso went back to basics with foreshortening but then galloped in the other direction with it, away from naturalism and toward subjectivism, turning the old medieval mutiple-angle foreshortening into a brand-new painting style called Cubism.
Where to find The birth of perspective art in Italy
Milan's sprawling 15C castle is home to several excellent museums, of tapestries, archaeological artifacts, paintings by Bellini and Mantegna, and sculptures from medieval to neoclassical—including Michelangelo's final sculpture, the Rondanini Pietà