Agricola arrives in Britain half way through the summer of 77AD. He would have been accompanied by his family and probably (as was usual for a provincial governor) by an advisory staff of companions (amici). It is probably that Frontinus had already left for no campaign was in progress and the army was relaxed.

Agricola likely first travelled to the provincial capital in London (Londinium) upon his arrival, where he would have met with his official staff (officium) and bodyguard, consisting of pedites and equites singulares. His agenda would have included liaising with the procurator, an equestrian officer responsible for financial matters. It’s reasonable to assume that Agricola carried with him orders (mandata) from Emperor Vespasian, echoing Claudius’ earlier directive to Aulus Plautius to ‘conquer the rest’ as recorded by Dio (60.21).

Word arrives that the Ordovices have just destroyed an ala stationed in their territory.

The Ordovices, shortly before Agricola’s arrival, had destroyed nearly the whole of a squadron of allied cavalry quartered in their territory.

Cornelius Tacitus: Agricola XVIII

Despite it being late in the summer and the troops being dispersed, Agricola who already knew the ground, decided to mount a punitive expedition against the tribesmen.

Meanwhile Agricola, though summer was past and the detachments were scattered throughout the province… He collected a force of veterans and a small body of auxiliaries

Cornelius Tacitus: Agricola XVIII

Agricola Defeats the Ordovices

Tacitus presents Agricola as a courageous and aggressive leader in a battle against the Ordovices. Agricola leads his force of veterans and auxiliaries and led them up a hill to confront the Ordovices, resulting in their near extermination.

then as the Ordovices would not venture to descend into the plain, he put himself in front of the ranks to inspire all with the same courage against a common danger, and led his troops up a hill. The tribe was all but exterminated.

Cornelius Tacitus: Agricola XVIII

The exact location of this battle is uncertain, though Dinas Dinorwig, near the Menai Strait, is a possible site. The name Dinorwig has been supposed to mean “fort of the Ordovices”.

Advance to The Island of Mona

Following this victory, Agricola aimed to seize the island of Mona, which the Romans had previously abandoned. Aware of the importance of capitalizing on his initial success to instil fear in other tribes, he planned to subjugate Mona. However, without a matured plan or a fleet, Agricola couldn’t immediately proceed. Agricola’s crossing of the Menai Strait showcased his military ingenuity. He led a surprise attack by auxiliaries, who were adept at swimming and managed to cross the strait without legionaries or boats. This unexpected manoeuvre demoralized the defenders on Mona, who had anticipated a more conventional assault by sea.

He formed the design of subjugating the island of Mona … But, as his plans were not matured, he had no fleet. … With some picked men of the auxiliaries, disencumbered of all baggage, who knew the shallows and had that national experience in swimming which enables the Britons to take care not only of themselves but of their arms and horses, he delivered so unexpected an attack that the astonished enemy who were looking for a fleet, a naval armament, and an assault by sea, thought that to such assailants nothing could be formidable or invincible.

Cornelius Tacitus: Agricola XVIII

Tacitus elsewhere notes that these specific soldiers originated from an island in the Rhine delta. This background accounted for their unique ability to swim, enabling them to cross the Rhine with their weapons and horses while maintaining formation (Hist. 4.12). In fact, when he mentions earlier in the same text that they had ‘enhanced their renown in Britain,’ he is likely referring to the four cohortes Batavorum and their military exploits under Agricola.

The exact location of this crossing is also unclear, but it may have been near Llanidan, accessible from Dinas Dinorwig. The auxiliary troops could have been Batavians, who were used to swimming alongside their horses, while in armour. This tactic had also been used by Aulus Plautius to cross the Medway.

Ultimately, Agricola’s actions led to the surrender of Mona and bolstered his reputation as a capable and respected Roman leader.