Borders of the Roman Empire in the context of "Roman mosaic"

Arabia Petraea (lit. 'Rocky Arabia') was a Roman province from the 2nd century to the 7th century. It was established after the Roman Empire conquered the Nabataean Kingdom in 106 and existed until the Muslim conquest of the Levant in the 630s. Spanning much of the Sinai Peninsula and part of the Levant, it was bordered by Syria to the north, by Judaea (later Syria Palaestina) to the west, and by Egypt to the southwest. To the east and southeast of Arabia Petraea was non-Roman territory that the Romans knew as Arabia Deserta. These two regions, together with a third region in South Arabia that was called Arabia Felix, accounted for the Arabian Peninsula in Roman geography.

Annexed by Trajan (r. 98–117), Arabia Petraea was a key province along the Limes Arabicus, which delineated the Roman Empire's borders throughout the Arabian Desert. It was also the only province in the Near East that the Romans did not gain and subsequently lose during Trajan's reign, unlike Armenia, Assyria, and Mesopotamia. The province's capital city was initially Petra, as it had been under the Nabataeans, but Bosra later served in this capacity. Most of the province's land was a vast desert that was sparsely populated by nomadic Arab tribes, though there were several urban settlements closer to the Jordan River.

Defensive walls are a feature of ancient Roman architecture. The Romans generally fortified cities, rather than building stand-alone 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.

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 defending the frontiers of the Empire by running 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. Most defences of the borders of the Roman Empire relied on systems of forts and roads without attempting a continuous barrier.

Limes (Latin; sg., pl.: limites) is a term used primarily for the Germanic border defence or delimiting system of ancient Rome marking the borders of the Roman Empire. The term has been extended in modern times to refer to the frontier defences in other parts of the empire, such as in the east and in Africa.

The Fossa Regia, also called the Fosse Scipio, was the first part of the Limes Africanus to be built in Roman Africa. It was used to divide the Berber kingdom of Numidia from the territory of Carthage that was conquered by the Romans in the second century BC.

It was an irregular ditch "from Thabraca on the northern coast to Thaenae on the south-eastern coast".

Fossatum Africae ("African ditch") is one or more linear defensive structures (sometimes called limes) claimed to extend over 750 km (470 mi) or more in northern Africa constructed during the Roman Empire to defend and control the southern borders of the Empire in Africa. It is considered to be part of the greater frontier system in Roman Africa.

It is considered to have many similarities of construction to Hadrian's Wall, one of the northern borders of the Empire in Britain.