The figures appear in a Roman style of dress and appearance, although their Christian elements, like the naked Adam and Eve, suggest it is a later Roman style.

The Corinthian columns and stylized pediment are orginially from pagan temples and would have been introduced to the Romans by the Greeks.

The work is from the middle of the fourth century and would have predated the height of Byzantium. 

Byzantine art evolved from ancient Roman art, although this transition is not superficially obvious. It is important to remember that the Byzantine Empire is at times referred to as the Eastern Roman Empire, and that the Byzantine people considered themselves to be Romans through the Fall of Constantinople in 1453. The evolution of style of Byzantine art occurred due to the fact that the Byzantine Empire and Constantinople were considered the bridge between Eastern and Western European cultures. The clash and intermingling of these cultures and religions is what created the unique style and appearance of Byzantine art.

David is the first instance in which there is a genuine blending of the Christian faith and the styles and forms of Classical figural art. Here is the first time that biblical figures are represented in the styles of the Classical masters. Yes, he is not the freestanding nudes we recognize- the Boxer, the Discus Thrower, those trim and muscled figures. David clings to the vestiges of Gothic figures, but he is nude and freestanding and has paved the way for more of his kind. 

Donatello had a clear interest in the human form. Many believed when he unveiled the piece that it had to have been done in life, it was so true to form. He also, though, was the first of his kind to use bronze in a freestanding nude (this hasn't been done since the Classical era). He is finally making a statement of Italian society, and the importance of blending Christian art and modernizing life.

This is David, also sculpted by artists like Donatello and Michelangelo. The head of Goliath sits at David's feet. John the Baptist was also beheaded, but by Salome, a woman. Hercules and Samson tend to be represented with more muscularity, and Moses is usually an older figure. 

Work is in the public domain, accessed through WikiArt: http://www.wikiart.org/en/andrea-del-verrocchio/david-1475

"Contrappusto" (meaning counterpose in Italian) is the term used to describe a posture in which the figure's weight is shifted to one foot, causing the shoulders and hips to twist off the body's central axis so they are no longer parallel, as seen in David. It was introduced in Classical Greek art and rediscovered in the Renaissance.

Equestrian statues, even when life-size, created a portrait of their subjects on massive scales. While commonplace in Rome, they were hardly made after the fall of Rome until the Renaissance, and in the age of absolutism in the seventeenth century, they were made all across Europe to commemorate and celebrate monarchs. These statues made the monarchs depicted in them appear intimidating, grandiose, and worthy of their position as absolute monarchs.

This work is Donatello's David. It predates the Davids of both Michelangelo as well as Bernini. Donatello was known among his colleagues for his freestanding work, and had in fact created a freestanding marble version of David that predates even this one. That David, though, was not nude where this one clearly is.