<P> The Romans generally fortified cities, rather than fortresses, but there are some fortified camps, such as the Saxon Shore forts like Porchester Castle in England . City walls were already significant in Etruscan architecture, and in the struggle for control of Italy under the early Republic many more were built, using different techniques . These included tightly - fitting massive irregular polygonal blocks, shaped to fit exactly in a way reminiscent of later Inca work . The Romans called a simple rampart wall an agger; at this date great height was not necessary . The Servian Wall around Rome was an ambitious project of the early 4th century BC . The wall was up to 10 metres (32.8 ft) in height in places, 3.6 metres (12 ft) wide at its base, 11 km (7 mi) long, and is believed to have had 16 main gates, though many of these are mentioned only from writings, with no other known remains . Some of it had a fossa or ditch in front, and an agger behind, and it was enough to deter Hannibal . Later the Aurelian Wall replaced it, enclosing an expanded city, and using more sophisticated designs, with small forts at intervals . </P> <P> The Romans walled major cities and towns in areas they saw as vulnerable, and parts of many walls remain incorporated in later defences, as at Córdoba (2nd century BC), Chester (earth and wood in the 70s AD, stone from c. 100), and York (from 70s AD). Strategic walls across open country were far rarer, and Hadrian's Wall (from 122) and the Antonine Wall (from 142, abandoned only 8 years after completion) are the most significant examples, both on the Pictish frontier . </P> <P> On his return from campaigns in Greece, the general Sulla brought back what is probably the most well - known element of the early imperial period, the mosaic, a decoration made of colourful chips of stone inserted into cement . This tiling method took the empire by storm in the late first century and the second century and in the Roman home joined the well known mural in decorating floors, walls, and grottoes with geometric and pictorial designs . </P> <P> There were two main techniques in Greco - Roman mosaic: opus vermiculatum used tiny tesserae, typically cubes of 4 millimeters or less, and was produced in workshops in relatively small panels which were transported to the site glued to some temporary support . The tiny tesserae allowed very fine detail, and an approach to the illusionism of painting . Often small panels called emblemata were inserted into walls or as the highlights of larger floor - mosaics in coarser work . The normal technique, however, was opus tessellatum, using larger tesserae, which were laid on site . There was a distinct native Italian style using black on a white background, which was no doubt cheaper than fully coloured work . </P>

Which was not a roman contribution to architecture