They were originally delineated and described by the German archaeologist August Mau (1840–1909) from the excavation of wall paintings at Pompeii, which is one of the largest groups of surviving Roman frescoes.
The four main styles of Roman wall painting defined are: structural (or incrustation), architectural, ornamental, and intricate.
The paintings sometimes contained depictions of life in this area prior to the great eruption that destroyed much of the countryside and the cities of Pompeii and Herculaneum.
[5] Other simulated elements (e.g. suspended alabaster discs in vertical lines, 'wooden' beams in yellow and 'pillars' and 'cornices' in white), and the use of vivid color, were considered signs of wealth.
This technique consists of highlighting elements to pass them off as three-dimensional realities – columns for example, dividing the wall-space into zones – and was a method widely used by the Romans.
The blocks were typically lined along the base of the wall and the actual picture was created on flat plaster.
They also added objects that are commonly seen in real life such as vases and shelves along with items that appeared to be sticking out of the wall.
The picture plane was pushed farther back into the wall by painted architectonic features such as Ionic columns or stage platforms.
Imitations of images appeared, at first in the higher section, then (after 50 BC) in the background of landscapes which provided a stage for mythological stories, theatrical masks, or decorations.
It leaves room for more figurative and colorful decoration, with an overall more ornamental feeling, and often presents great finesse in execution.
It obeyed strict rules of symmetry dictated by the central element, dividing the wall into three horizontal and three to five vertical zones.
The vertical zones would be divided up by geometric motifs or bases, or slender columns of foliage hung around candelabra.
Plants and characteristically Egyptian animals were often introduced, part of the Egyptomania in Roman art after Augustus' defeat of Cleopatra and annexation of Egypt in 30 BC.
These paintings were decorated with delicate linear fantasies, predominantly monochromatic, that replaced the three-dimensional worlds of the Second Style.
Also included in this style are paintings similar to the one found in Cubiculum 15 of the Villa of Agrippa Postumus in Boscotrecase (c. 10 BC).
These involve a delicate architectural frame over a blank, monochromatic background with only a small scene located in the middle, like a tiny floating landscape.
All four styles of wall painting were developed prior to the eruption of Mount Vesuvius in 79 AD, which covered Pompeii in ash.