Although comparatively little survives, there are some magnificent examples (such as Villa Livia frescoes of an imaginary garden) in the Museo Nazionale Romano collection at Palazzo Massimo alle Terme in Rome and in the Museo Nazionale Archeologico in Naples. Traces of mosaics and frescos in situ can be found at Rome's ancient port of Ostia, as well as at Pompeii and the ancient town of Herculaneum.

EARLY CHRISTIAN & BYZABTINE

The early Christians practised their religion in private houses (many of which later became churches) and catacombs. In the 4th century, under the Christian emperor Constantine, several places of worship were constructed - the architecture based on the buildings of Imperial Rome, in particular the rectangular basilica or public hall. Over time, transepts were added to create the shape of a cross.

The domed baptistery of San Giovanni in Laterano (in Rome), built by Constantine between 315 and 324 and remodelled into its present octagonal shape in the 5th century, became the model for many baptisteries throughout the Christian world. The starkly simple Basilica of Santa Sabina in Rome, built in the 5th century,  is one of the best presented churches of the period.

In 402, Ravenna became the imperial capital and several churches were built there, some in the basilica style. The Bysantine dome was freely adopted, often supported on a square (rather than round as the Romans had used) base. The innovative plan for the town's Basilica di San Vitale used an octagon within an octagon.

The Byzantine architectural style reached its peak in Venice, with  the magnificent St Mark's Basilica (consecrated in 1094). Although the church as you see it today betrays a mix of styles (with some Romanesque and later Renaissance elements), it has a markedly eastern air. The bubbled roof of domes and the inclusion of a narthex, a kind of lobby you pass through before entering the church proper, are just two such distinctive elements.

In the 10th and 11th centuries, the Greeks in the south built several small, cross-shaped and domed churches in the Byzantine style.

Roman painting went into decline form the 2nd century AD, when mosaics and coloured marble veneers became a popular decorative medium.                                                                            

Mosaics in St Mark's Basilica (Venice)

At first, black-and-white mosaic cubes where used for floors in both public and private buildings. Later, coloured stones were employed, as in the villa at Piazza Armerina, south of Enna on Sicily, and in the early churches of Aquileia and Gardo, near Trieste.

By the 4th century, glass tesserae (mosaic tiles) were used to splendid effect in the apses of the early Christian churches of Rome (such as the Basilica of Santa Maggiore) and Ravenna (Mausoleo di Galla Placidia, the Basilica di San Vitale and the Basilica di Sant'Apollinare Nuovo).

During the 5th and 6th centuries art was an instrument for the propagation and maintenance of the faith. At first restricted to depictions of Christ and other holy figures such as the Virgin Mary, saints and angels, the range of images broadened to include more complex themes and scenes from the Old Testament and the Passion of Christ.

In those parts of Italy that continued to be influenced by Byzantium, the art of mosaics continued to develop in splendour. To walk into St Mark's Basilica in Venice is to be swallowed by a shimmering sea of gold and colour. Work fist started on these mosaics in the 11th century and continued long after. Some of them were done as late as the 15th century, when other artistic styles and mediums had long taken pre-eminence elsewhere in Italy. The oldest cathedral in the Venetian lagoon, Santa Maria Assunta on the island of Torcello, is home to magnificent mosaics. The one depicting the Last Judgement is extraordinary for its detail and symbolic density.

At the other end of the country, Byzantine artists were called in to decorate the interior of the splendid Norman cathedral of Monreale, outside Palermo on Sicily. The result is a splendid Christ Pantocrator dominating a series of Old and New Testament scenes.

The early Christian period saw an almost total rejectionn of sculpture, except for carved decoration on sarcophagi. The carved wooden panels depicting scenes of the Passion of Christ on the doors of the Basilica di Santa Sabina in Rome, dating from the 5th century, are a significant but rare exception, only with the arrival of a new architectural and decorative style, Romanesque, would sculpture recover its importance.

St Mark's Basilica (Venice)