This fresco, painted on the walls of Santa Maria Novella in Florence, is considered to be Masaccio's masterpiece. The patrons who commissioned the work are shown kneeling at the forefront of the painting, however they cannot be identified with certainty. The painting depicts the crucifixion of Christ, with the customary figures of the Virgin and St John at the foot of the cross. However, the scene defies Renaissance convention in so many ways that it has remained an enigma, despite being studied by scholars for hundreds of years. The painting is known as The Holy Trinity (Santa Trinità) due to its depiction of Christ with God behind him, and the white dove of the Holy Spirit hovering between their heads. Although a figurative depiction of God was not a religious taboo at the time, he would usually have been depicted in a non-earthly realm, representing the heavens, rather than in the concrete space of the church. 

This Fresco is in the  Church of Santa Maria Novella, Florence 

The rendering of three-dimensional space in this painting is often considered to represent the pinnacle of Masaccio's technical mastery. The perspective is so accurate that modern scholars have been able to digitally construct the fictional space depicted in the painting as a 3D model. The fine draughtsmanship that allowed Masaccio to create such a realistic space gives the sense that the crucifixion is taking place right in front of the viewer's eyes, in the church itself. This lends the image an immediacy that instantly connects the viewer with Christ's suffering, not only as a God but as a fellow person. 

The depiction of God as a Father, standing behind his son, allows the viewer to relate to the Holy Trinity on a more human level, a radical act at a time in which the Catholic Church had a strict hierarchy that insisted the public could only connect with God through priests chosen by the Church. It is suggestive of the new humanist phase in art and philosophy that was beginning to be ushered in with the Early Renaissance. The fictional architecture of the space does however incorporate degrees of separation. God is above and behind Jesus, who is above the saints, the donors are close to God by virtue of their generosity to the church, and the viewer stands below the scene looking in. At eye level, and 'beneath' the paintings fictional ground, is a naturalistic image of a tomb with a skeleton lying on top of it. Carved into the tomb in Italian is the phrase "I was once what you are, and what I am you shall be". This speaks directly to the viewer of their mortality, as they gaze up at the image of Christ dying for their salvation.