Between 55 BC and the 40s AD, the status quo of tribute, hostages, and client states without direct military occupation, begun by Caesar's invasions of Britain, largely remained intact.

[16] According to Augustus's Res Gestae, two British kings, Dubnovellaunus and Tincomarus, fled to Rome as supplicants during his reign,[17] and Strabo's Geographica, written during this period, says Britain paid more in customs and duties than could be raised by taxation if the island were conquered.

[19][20] Caligula may have planned a campaign against the Britons in AD 40, but its execution was unclear: according to Suetonius' The Twelve Caesars, he drew up his troops in battle formation facing the English Channel and, once his forces had become quite confused, ordered them to gather seashells, referring to them as "plunder from the ocean due to the Capitol and the Palace".

In 43, possibly by reassembling Caligula's troops from 40, Claudius mounted an invasion force under overall charge of Aulus Plautius, a distinguished senator.

Cassius Dio mentions Gnaeus Hosidius Geta, who probably led the IX Hispana, and Vespasian's brother Titus Flavius Sabinus the Younger.

In any case a new ruler for their region, Cogidubnus, soon appeared as his heir and as king of a number of territories following the first stage of the conquest as a reward as a Roman ally.

[34] Legio IX Hispana was sent north towards Lincoln (Latin: Lindum Colonia) and by 47 it is likely that an area south of a line from the Humber to the Severn Estuary was under Roman control.

That this line is followed by the Roman road of the Fosse Way has led many historians to debate the route's role as a convenient frontier during the early occupation.

Late in 47 the new governor of Britain, Publius Ostorius Scapula, began a campaign against the tribes of modern-day Wales, and the Cheshire Gap.

Caratacus himself led this guerilla campaign but was defeated when he finally chose to offer a decisive battle; he fled to the Roman client tribe of the Brigantes who occupied the Pennines.

Ostorius died and was replaced by Aulus Didius Gallus who brought what are now the Welsh borders under control but did not move further north or west, probably because Claudius was keen to avoid what he considered a difficult and drawn-out war for little material gain in the mountainous terrain of upland Britain.

When Nero became emperor in 54, he seems to have decided to continue the invasion and appointed Quintus Veranius as governor, a man experienced in dealing with the troublesome hill tribes of Anatolia.

Veranius and his successor Gaius Suetonius Paulinus mounted a successful campaign across North Wales, famously killing many druids when he invaded the island of Anglesey in 60.

[35] Her husband was Venutius; one speculation is that he might have been a Carvetian and may therefore have been responsible for the incorporation of Cumbria into a Brigantian federation whose territory straddled Britain along the Solway-Tyne line.

[38] From other sources, it seems that Bolanus had possibly dealt with Venutius and penetrated into Scotland, and evidence from the carbon-dating of the gateway timbers of the Roman fort at Carlisle (Luguvalium) suggests that they were felled in AD 72, during the governorship of Cerialis.

[39] Nevertheless, Gnaeus Julius Agricola played his part in the west as commander of the legion XX Valeria Victrix (71–73), while Cerialis led the IX Hispania in the east.

The western thrust was started from Lancaster, where there is evidence of a Cerialian foundation, and followed the line of the Lune and Eden river valleys through Low Borrow Bridge and Brougham (Brocavum).

[40] At some point between 72 and 73, part of Cerialis's force moved across the Stainmore Pass from Corbridge westwards to join Agricola, as evidenced by campaign camps (which may have been previously set up by Bolanus) at Rey Cross, Crackenthorpe, Kirkby Thore and Plumpton Head.

Arriving in mid-78, Agricola completed the conquest of Wales in defeating the Ordovices[42] who had destroyed a cavalry ala of Roman auxiliaries stationed in their territory.

[43] The following year he moved against the Brigantes of northern England and the Selgovae along the southern coast of Scotland, using overwhelming military power to establish Roman control.

In southernmost Caledonia, the lands of the Selgovae (approximating to modern Dumfriesshire and the Stewartry of Kirkcudbright) were heavily planted with forts, not only establishing effective control there, but also completing a military enclosure of south-central Scotland (most of the Southern Uplands, Teviotdale, and western Tweeddale).

The fortress at Inchtuthil was dismantled before its completion and the other fortifications of the Gask Ridge in Perthshire, erected to consolidate the Roman presence in Scotland in the aftermath of Mons Graupius, were abandoned within the space of a few years.

It is equally likely that the costs of a drawn-out war outweighed any economic or political benefit and it was more profitable to leave the Caledonians alone and only under de jure submission.

With the decline of imperial ambitions in Scotland (and Ireland) by AD 87 (the withdrawal of the 20th legion), consolidation based on the line of the Stanegate road (between Carlisle and Corbridge) was settled upon.

[36]: 58  Apart from the Stanegate line, other forts existed along the Solway Coast at Beckfoot, Maryport, Burrow Walls (near the present town of Workington) and Moresby (near Whitehaven).

The Selgovae, having settled in the regions of present-day Kirkcudbrightshire and Dumfriesshire immediately northwest of Hadrian's Wall, were amongst the first of the Caledonian tribes to face Lollius Urbicus's legions together with the Otadini.

The Romans, who were well versed in warfare on hilly terrain since their founding, moved quickly to occupy strategic points and high ground, some of which had already been fortified by the Caledonians with hill forts.

According to Dio Cassius, he inflicted genocidal depredations on the natives and incurred the loss of 50,000 of his own men to the attrition of guerrilla tactics before having to withdraw to Hadrian's Wall.

Little is known of his campaigns with scant archaeological evidence, but fragmentary historical sources suggest he reached the far north of Britain and won a major battle in early summer before returning south.

[59][60] Later excursions into Scotland by the Romans were generally limited to the scouting expeditions of exploratores in the buffer zone that developed between the walls, trading contacts, bribes to purchase truces from the natives, and eventually the spread of Christianity.