In this painting, the lines of perspective draw the eye in to the middle of the image. I couldn't find a great deal of information at a cursory glance, but based on the title, I believe it is about Caeser's pardoning of Brutus following his surrender at the Battle of Pharsalus, which was an important point in the civil war in 49 BC.
5 years later, Brutus would lead upwards of 60 senators (conspirators, or to some, liberators) to assassinate Caeser. There reasoning - if no one could tell who struck the death blow, no one man could be held responsible. They hated Caeser so much that they ended up hurting each other trying to stab him, Brutus himself was said to have been stabbed in the arm and leg.