Roman military frontiers and fortifications

The borders of the Roman Empire, which fluctuated throughout the empire's history, were realised as a combination of military roads and linked forts, natural frontiers and man-made fortifications which separated the lands of the empire from the countries beyond.

The Rhine is one of the major European rivers. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein, Swiss-Austrian, and Swiss-German borders. After that the Rhine defines much of the Franco-German border, after which it flows in a mostly northerly direction through the German Rhineland. Finally in Germany the Rhine turns into a predominantly westerly direction and flows into the Netherlands where it eventually empties into the North Sea. It drains an area of 9,973 sq km and its name derives from the Celtic Rēnos. There are also two German states named after the river, North Rhine-Westphalia and Rhineland-Palatinate.

The Danube is the second-longest river in Europe, after the Volga in Russia. It flows through much of Central and Southeastern Europe, from the Black Forest into the Black Sea. A large and historically important river, it was once a frontier of the Roman Empire and today connects ten European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for 2,850 km (1,770 mi), passing through or bordering Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova, and Ukraine. Among the many cities on the river are four national capitals: Vienna, Budapest, Belgrade and Bratislava. Its drainage basin amounts to 817 000 km² and extends into nine more countries.

A barbarian, or savage, is someone who is perceived to be either uncivilized or primitive. The designation is usually applied as a generalization based on a popular stereotype; barbarians can be members of any nation judged by some to be less civilized or orderly but may also be part of a certain "primitive" cultural group or social class both within and outside one's own nation. Alternatively, they may instead be admired and romanticised as noble savages. In idiomatic or figurative usage, a "barbarian" may also be an individual reference to a brutal, cruel, warlike, and insensitive person.

Caligula, formally known as Gaius, was the third Roman emperor, ruling from AD 37 until his assassination in AD 41. He was the son of the Roman general Germanicus and Agrippina the Elder, Augustus' granddaughter. Caligula was born into the first ruling family of the Roman Empire, conventionally known as the Julio-Claudian dynasty.

Hadrian was Roman emperor from 117 to 138. He was born in Italica, a Roman municipium founded by Italic settlers in Hispania Baetica. He came from a branch of the gens Aelia that originated in the Picenean town of Hadria, the Aeli Hadriani. His father was of senatorial rank and was a first cousin of Emperor Trajan. Hadrian married Trajan's grand-niece Vibia Sabina early in his career before Trajan became emperor and possibly at the behest of Trajan's wife Pompeia Plotina. Plotina and Trajan's close friend and adviser Lucius Licinius Sura were well disposed towards Hadrian. When Trajan died, his widow claimed that he had nominated Hadrian as emperor immediately before his death.

Līmes is a modern term used primarily for the Germanic border defence or delimiting system of Ancient Rome marking the borders of the Roman Empire, but it was not used by the Romans for that purpose. The term has been extended to refer to the frontier defences in other parts of the empire, such as in the east and in Africa.

Segedunum was a Roman fort at modern-day Wallsend, North Tyneside in North East England. The fort lay at the eastern end of Hadrian's Wall near the banks of the River Tyne, forming the easternmost portion of the wall. It was in use as a garrison for approximately 300 years, from around 122 AD, almost up to 400AD. Today, Segedunum is the most thoroughly excavated fort along Hadrian's Wall, and is operated as Segedunum Roman Fort, Baths and Museum. It forms part of the Hadrian's Wall UNESCO World Heritage Site.

Hadrian's Wall, also known as the Roman Wall, Picts' Wall, or Vallum Hadriani in Latin, is a former defensive fortification of the Roman province of Britannia, begun in AD 122 in the reign of the Emperor Hadrian. Running from Wallsend on the River Tyne in the east to Bowness-on-Solway in the west of what is now northern England, it was a stone wall with large ditches in front of it and behind it that crossed the whole width of the island. Soldiers were garrisoned along the line of the wall in large forts, smaller milecastles and intervening turrets. In addition to the wall's defensive military role, its gates may have been customs posts.

Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe. With an area of 209,331 km2 (80,823 sq mi), it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is dominated by a maritime climate with narrow temperature differences between seasons. The 60% smaller island of Ireland is to the west—these islands, along with over 1,000 smaller surrounding islands and named substantial rocks, form the British Isles archipelago.

The frontier of the Roman Empire in Britain is sometimes styled Limes Britannicus by authors for the boundaries, including fortifications and defensive ramparts, that were built to protect Roman Britain. These defences existed from the 1st to the 5th centuries AD and ran through the territory of present-day England, Scotland and Wales.

The Great Wall of China is a series of fortifications that were built across the historical northern borders of ancient Chinese states and Imperial China as protection against various nomadic groups from the Eurasian Steppe. Several walls were built from as early as the 7th century BC, with selective stretches later joined by Qin Shi Huang (220–206 BC), the first emperor of China. Little of the Qin wall remains. Later on, many successive dynasties built and maintained multiple stretches of border walls. The best-known sections of the wall were built by the Ming dynasty (1368–1644).

Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe. With an area of 209,331 km2 (80,823 sq mi), it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is dominated by a maritime climate with narrow temperature differences between seasons. The 60% smaller island of Ireland is to the west—these islands, along with over 1,000 smaller surrounding islands and named substantial rocks, form the British Isles archipelago.

Caledonia was the Latin name used by the Roman Empire to refer to the part of Great Britain that lies north of the River Forth, which includes most of the land area of Scotland. Today, it is used as a romantic or poetic name for all of Scotland. During the Roman Empire's occupation of Scotland, the area they called Caledonia was physically separated from the rest of the island by the Antonine Wall. The Romans several times invaded and occupied it, but unlike the rest of the island, it remained outside the administration of Roman Britain.

The Central Belt of Scotland is the area of highest population density within Scotland. Depending on the definition used, it has a population of between 2.4 and 4.2 million, including Greater Glasgow, Ayrshire, Falkirk, Edinburgh, Lothian and Fife.

The Picts were a group of peoples who lived in Britain north of the Forth–Clyde isthmus in the Pre-Viking, Early Middle Ages. Where they lived and details of their culture can be inferred from early medieval texts and Pictish stones. The term Picti appears in written records as an exonym from the late third century CE, but was adopted as an endonym in the late seventh century during the Verturian hegemony. This lasted around 160 years until the succession of the Alpínid dynasty, when the Pictish kingdom merged with that of Dál Riata to form the Kingdom of Alba. The concept of "Pictish kingship" continued for a few decades until it was abandoned entirely as a contemporary signifier during the reign of Caustantín mac Áeda.

Hadrian's Wall, also known as the Roman Wall, Picts' Wall, or Vallum Hadriani in Latin, is a former defensive fortification of the Roman province of Britannia, begun in AD 122 in the reign of the Emperor Hadrian. Running from Wallsend on the River Tyne in the east to Bowness-on-Solway in the west of what is now northern England, it was a stone wall with large ditches in front of it and behind it that crossed the whole width of the island. Soldiers were garrisoned along the line of the wall in large forts, smaller milecastles and intervening turrets. In addition to the wall's defensive military role, its gates may have been customs posts.

The Gask Ridge is the modern name given to an early series of fortifications, built by the Romans in Scotland, close to the Highland Line. Modern excavation and interpretation has been pioneered by the Roman Gask Project, with Birgitta Hoffmann and David Woolliscroft. The ridge fortifications: forts, fortlets and watchtowers were only in operation for a short number of years, probably a single digit number.

The Antonine Wall, known to the Romans as Vallum Antonini, was a turf fortification on stone foundations, built by the Romans across what is now the Central Belt of Scotland, between the Firth of Clyde and the Firth of Forth. Built some twenty years after Hadrian's Wall to the south, and intended to supersede it, while it was garrisoned it was the northernmost frontier barrier of the Roman Empire. It spanned approximately 63 kilometres and was about 3 metres high and 5 metres wide. Lidar scans have been carried out to establish the length of the wall and the Roman distance units used. Security was bolstered by a deep ditch on the northern side. It is thought that there was a wooden palisade on top of the turf. The barrier was the second of two "great walls" created by the Romans in Great Britain in the second century AD. Its ruins are less evident than those of the better-known and longer Hadrian's Wall to the south, primarily because the turf and wood wall has largely weathered away, unlike its stone-built southern predecessor.

A milecastle was a small fort (fortlet), a rectangular fortification built during the period of the Roman Empire. They were placed at intervals of approximately one Roman mile along several major frontiers, for example Hadrian's Wall in Great Britain, hence the name.

The Danube is the second-longest river in Europe, after the Volga in Russia. It flows through much of Central and Southeastern Europe, from the Black Forest into the Black Sea. A large and historically important river, it was once a frontier of the Roman Empire and today connects ten European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for 2,850 km (1,770 mi), passing through or bordering Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova, and Ukraine. Among the many cities on the river are four national capitals: Vienna, Budapest, Belgrade and Bratislava. Its drainage basin amounts to 817 000 km² and extends into nine more countries.

Dacia was the land inhabited by the Dacians, its core in Transylvania, stretching to the Danube in the south, the Black Sea in the east, and the Tisza in the west. The Carpathian Mountains were located in the middle of Dacia. It thus roughly corresponds to the present-day countries of Romania, as well as parts of Moldova, Bulgaria, Serbia, Hungary, Slovakia, and Ukraine.

Germania Inferior was a Roman province from AD 85 until the province was renamed Germania Secunda in the fourth century, on the west bank of the Rhine bordering the North Sea. The capital of the province was Colonia Claudia Ara Agrippinensium.

Germania Superior was an imperial province of the Roman Empire. It comprised an area of today's western Switzerland, the French Jura and Alsace regions, and southwestern Germany. Important cities were Besançon (Vesontio), Strasbourg (Argentoratum), Wiesbaden, and Germania Superior's capital, Mainz (Mogontiacum). It comprised the Middle Rhine, bordering on the Limes Germanicus, and on the Alpine province of Raetia to the south-east. Although it had been occupied militarily since the reign of Augustus, Germania Superior was not made into an official province until c. 85 AD.

The Euphrates is the longest and one of the most historically important rivers of Western Asia. Together with the Tigris, it is one of the two defining rivers of Mesopotamia. Originating in Turkey, the Euphrates flows through Syria and Iraq to join the Tigris in the Shatt al-Arab, which empties into the Persian Gulf.

The Parthian Empire, also known as the Arsacid Empire, was a major Iranian political and cultural power in ancient Iran from 247 BC to 224 AD. Its latter name comes from its founder, Arsaces I, who led the Parni tribe in conquering the region of Parthia in Iran's northeast, then a satrapy (province) under Andragoras, who was rebelling against the Seleucid Empire. Mithridates I (r. c. 171–132 BC) greatly expanded the empire by seizing Media and Mesopotamia from the Seleucids. At its height, the Parthian Empire stretched from the northern reaches of the Euphrates, in what is now central-eastern Turkey, to present-day Afghanistan and western Pakistan. The empire, located on the Silk Road trade route between the Roman Empire in the Mediterranean Basin and the Han dynasty of China, became a center of trade and commerce.

Iran, officially the Islamic Republic of Iran and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmenistan to the north, by Afghanistan and Pakistan to the east, and by the Gulf of Oman and the Persian Gulf to the south. It covers an area of 1.64 million square kilometres, making it the 17th-largest country. Iran has an estimated population of 86.8 million, making it the 17th-most populous country in the world, and the second-largest in the Middle East. Its largest cities, in descending order, are the capital Tehran, Mashhad, Isfahan, Karaj, Shiraz, and Tabriz.

Iraq, officially the Republic of Iraq, is a country in Western Asia. It is bordered by Turkey to the north, Iran to the east, the Persian Gulf and Kuwait to the southeast, Saudi Arabia to the south, Jordan to the southwest and Syria to the west. The capital and largest city is Baghdad. Iraq is home to diverse ethnic groups; mostly Arabs, as well as Kurds, Turkmens, Assyrians, Armenians, Yazidis, Mandaeans, Persians and Shabakis with similarly diverse geography and wildlife. The majority of the country's 40 million residents are Muslims – the notable other faiths are Christianity, Yazidism, Mandaeism, Yarsanism and Zoroastrianism. The official languages of Iraq are Arabic and Kurdish; others also recognised in specific regions are Suret (Assyrian), Turkish and Armenian.

Parthia is a historical region located in northeastern Greater Iran. It was conquered and subjugated by the empire of the Medes during the 7th century BC, was incorporated into the subsequent Achaemenid Empire under Cyrus the Great in the 6th century BC, and formed part of the Hellenistic Seleucid Empire after the 4th-century BC conquests of Alexander the Great. The region later served as the political and cultural base of the Eastern Iranian Parni people and Arsacid dynasty, rulers of the Parthian Empire. The Sasanian Empire, the last state of pre-Islamic Iran, also held the region and maintained the seven Parthian clans as part of their feudal aristocracy.

Ctesiphon was an ancient city, located on the eastern bank of the Tigris, about 35 kilometres (22 mi) southeast of present-day Baghdad. Ctesiphon served as a royal capital of the empires in the Parthian and Sasanian eras for over eight hundred years. Ctesiphon was capital of the Sasanian Empire from 226–637 until the Muslim conquest of Persia in 651 AD.

Assyria was a major ancient Mesopotamian civilization which existed as a city-state from the 21st century BC to the 14th century BC, then to a territorial state, and eventually an empire from the 14th century BC to the 7th century BC.

Babylonia was an ancient Akkadian-speaking state and cultural area based in the city of Babylon in central-southern Mesopotamia. It emerged as an Amorite-ruled state c. 1894 BC. During the reign of Hammurabi and afterwards, Babylonia was called "the country of Akkad", a deliberate archaism in reference to the previous glory of the Akkadian Empire. It was often involved in rivalry with the older state of Assyria to the north and Elam to the east in Ancient Iran. Babylonia briefly became the major power in the region after Hammurabi created a short-lived empire, succeeding the earlier Akkadian Empire, Third Dynasty of Ur, and Old Assyrian Empire. The Babylonian Empire rapidly fell apart after the death of Hammurabi and reverted to a small kingdom.

Osroes I was a Parthian contender, who ruled the western portion of the Parthian Empire from 109 to 129, with a one-year interruption. For most of his reign he contended with the rival king Vologases III who was based in the eastern provinces. In 116, Osroes I was briefly ousted from his throne at Ctesiphon during an invasion by Roman emperor Trajan, who installed Osroes' son, Parthamaspates. After Trajan's death the following year, Osroes I's rule was reinstated by the Parthian nobility. In 129, he was removed from power by Vologases III.

Assyria was a short-lived Roman province in Mesopotamia that was created by Trajan in 116 during his campaign against the Parthian Empire. After Trajan's death, the newly proclaimed emperor Hadrian ordered the evacuation of Assyria in 118.

Mesopotamia is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the Fertile Crescent. Today, Mesopotamia occupies modern Iraq. In the broader sense, the historical region included present-day Iraq and parts of present-day Iran, Kuwait, Syria and Turkey.

The Siwa Oasis is an urban oasis in Egypt; between the Qattara Depression and the Great Sand Sea in the Western Desert, 50 km (30 mi) east of the Libyan border, and 560 km (348 mi) from the capital. Its fame primarily from its ancient role as the home to an oracle of Ammon, the ruins of which are a popular tourist attraction which gave the oasis its ancient name Oasis of Amun Ra, a major Egyptian deity.

The Nile is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest river in the world, though this has been contested by research suggesting that the Amazon River is slightly longer. Of the world's major rivers, the Nile is one of the smallest, as measured by annual flow in cubic metres of water. About 6,650 km (4,130 mi) long, its drainage basin covers eleven countries: the Democratic Republic of the Congo, Tanzania, Burundi, Rwanda, Uganda, Kenya, Ethiopia, Eritrea, South Sudan, Republic of the Sudan, and Egypt. In particular, the Nile is the primary water source of Egypt, Sudan and South Sudan. Additionally, the Nile is an important economic river, supporting agriculture and fishing.

The Limes Mauretaniae was a portion of a 4,000-kilometre (2,500 mi) Roman fortified border (limes) in Africa approximately 100 kilometres (62 mi) south of the modern day Algiers.

Arabia Petraea or Petrea, also known as Rome's Arabian Province or simply Arabia, was a frontier province of the Roman Empire beginning in the 2nd century. It consisted of the former Nabataean Kingdom in Jordan, southern Levant, the Sinai Peninsula and northwestern Arabian Peninsula. Its capital was Petra. It was bordered on the north by Syria, on the west by Judaea and Egypt, and on the south and east by the rest of Arabia, known as Arabia Deserta and Arabia Felix.

The Limes Tripolitanus was a frontier zone of defence of the Roman Empire, built in the south of what is now Tunisia and the northwest of Libya. It was primarily intended as a protection for the tripolitanian cities of Leptis Magna, Sabratha and Oea in Roman Libya.

Fossatum Africae is one or more linear defensive structures 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.