Graeco-Roman period
Mosaics are designs or pictures created by a collocation of pieces of marble, glass, pebbles, ceramic material, or precious stone embedded in cement or other form of fixative.   Though the history of mosaic can be traced back to more than 4,000 years ago, the earlier works tend to be unstructured decoration, mostly pebble pavements using different colored stones to create patterns.
Mosaic floors and walls were extremely popular in all centers of ancient Greek, Cretan, Etruscan and Roman civilization. Methods used and materials employed didn't change much until the renaissance. Stone tiles then gradually replaced clay tiles.
Roman terrazzo pavement, Forum Romanum, Rome (2000 BC)
Detail of a mosaic from Pella, the hunt for the stag, 400 BC.
The practice of this decorative art form was first perfected by the ancient Greeks, who made their first mosaics with small pebbles, depicting their gods. The Greeks saw mosiac making as a creative form of art expression, since the word "mosaic" comes from the Greek term "muse", the goddesses of artistic inspiration.
Neptune and the four seasons
2nd c. AD (Bardo Museum)
The Romans were sophisticated architects and builders.
Tile mosaic in de "Dom Morano".
By around 200 BC, specially manufactured pieces ("tesserae") were being used to give extra detail and range of color to the work. Because of tesserae's smaller size compared to pebbles, more could be packed into a given area. As similar to printed pictures, the more dots, the more detailed resolution. This led to designs of ever greater detail and complexity. Using small tesserae, sometimes only a few millimeters in size, mosaic artists were able to create painting-like pictures. Adding to the precise geometric patterns and detailed scenes of characters and animals, the Romans succeeded the Greeks and further developed mosaic techniques with the use of marble cubes and glass tesserae. The expansion of the Roman Empire proliferated mosaics as these artistic works are found throughout the Roman Empire from Britain to North Africa. Some of the earliest 2nd and 1st century mosaics have been found preserved at Pompeii. Even the pavements were decorated with stone and marble patterns, much like today’s doormats. Considering the violent nature of Pompeii's end it is remarkable that such treasures have survived. The picture on the left is of a domestic mosaic. Many of these ancient mosaics survived the ravages of time remarkably well. Because of its enduring characteristics, mosaic art has also been called the eternal art form.
National Archeological Museum in Naples.
Domestic Mosaic from Popeii
The crowning of Venus
4th c. AD (Bardo Museum)
 
 
Paleo Christians Period
In the early Christian periods an enormous amount of highly-sophisticated glass tesserae works were produced. With the legalization of Christianity in the 4th century AD, as the great building boom in churches followed, mosaic became a medium to engage and instruct the viewers to Christian art. Its application was beyond simple church decoration- it told visual stories from the Bible, much like today’s comic strips, to an audience that was primarily illiterate. There are many examples to be found in Europe, such as the Norman mosaics at the cathedral in Monreale, Sicily. Such works, inspired by lively use of mosaic color, form and treatment to narrate scenes from the sacrifice of Isaac, Noah’s Arch, and encompassed many other great Bible stories. The earliest work of such kind though, such as those of the first basilica of St. Peter and St. Paul, was all destroyed. The earliest surviving examples are the 5th century mosaics in the church of Santa Maria Maggiore in Rome. Constructed of small cubed tesserae of glass paste, these mosaic works depicts events of the Old Testament and the New Testament.

At Ravenna, Italy, the mosaic work in the various churches is the pinnacle of its period. Of which the baptistery of the cathedral dedicated to St. John is an especially good illustration, the church being originally built at the end of the fourth century but burnt in 434. The mosaics of the Mausoleum of Galla Placidia (450) are also of excellent design and workmanship.