The painting shows San Marco who is saving a slave from his pagan lord who wants to kill him.
The scene takes place under a pergola and in the background we can see a square and behind it a garden. The perspective converges towards the centre and the horizon line is high as if the spectator was watching from an elevated point.
The main characters are three: the slave on the floor with the broken torture instruments, an old person on the right side who is watching these instruments and San Marco on the top who can be seen only by the spectators and not by the protagonists of the painting.
The crowd moves from left to right: people on the left hang out to see the scene, people on the right back down.
The colour in the foreground is violent and pasty to give volume to the bodies, while in the background is faint to increase the perspective effect.
The protagonist is the light that has different intensities in the painting: it is vivid and natural in the backstage, dark under the pergola where the tragedy is taking place and unnatural and divine around San Marco.
In this painting, even if it is one of the first realized by the author, it is clear the great ability of Tintoretto in the use of the light. He highlights the characters and throws them in the scenic space of the painting.