The Roman conquest of Anglesey refers to two separate invasions of Anglesey in North West Wales that happened during the early years of the Roman conquest of Britain in the 1st century CE. The first invasion of North Wales began after the Romans had conquered much of southern Britain. It was led by the governor of Britannia, Suetonius Paulinus, who led a successful attack on the island in 60–61 CE. However, he had to leave because of the Boudican revolt. In 77 CE, Gnaeus Julius Agricola completely controlled the island, making it part of the Roman Empire until the end of Roman rule in Britain in the early 5th century CE. Anglesey was invaded because it was an important place for Celtic Druids and their religious practices, which made it a center of resistance against Roman rule.
No Roman records from that time mention Anglesey, which was called Mona in Latin and is still known as Môn in modern Welsh. Archaeologists have found a fort near Cemlyn Bay that was built shortly after the first invasion, a trading settlement near the Menai Strait, and a group of small homes built together on a hill for protection. In the final years of Roman rule in Britain, several military forts were built along the northern and western coasts to protect the island from attacks by sea raiders from Ireland. However, despite more than 300 years of Roman control, archaeologists have not found evidence of large cities or villas on the island, showing that Roman culture had less influence there than in other parts of Britain.
The only Roman account of the two invasions of Anglesey comes from the Roman historian Tacitus. His work, The Annals, which describes the history of the Roman Empire from Tiberius to Nero, mentions the first invasion led by Suetonius Paulinus. The second invasion is described in Tacitus’s Life of Gnaeus Julius Agricola, a book written to honor Agricola, Tacitus’s father-in-law. Tacitus may have used information from Agricola, who was present with the Roman forces during both invasions.
First invasion (60 CE)
The first invasion of Anglesey happened in 60 or 61 CE after Suetonius Paulinus successfully defeated British tribes and built Roman forts in other parts of the province. Tacitus wrote that Britain was under Suetonius Paulinus’s control. He was a skilled general who compared to Corbulo and aimed to achieve the same glory as recovering Armenia by defeating Rome’s enemies. He planned to attack Mona, now called Anglesey, which had a strong population and was a place where people fleeing from battles could hide. Tacitus, who later married the daughter of Suetonius Paulinus’s assistant, Gnaeus Julius Agricola, may have learned about the campaign directly from Suetonius or others involved.
The decision to invade Anglesey might have been influenced by reports about copper mines on the island.
Tacitus described how Suetonius built flat-bottomed boats to help soldiers cross shallow and uncertain waters. Soldiers marched across the water, while cavalry followed by swimming or wading where the water was deep.
It is unclear where these boats were built, but some evidence suggests they might have come from Deva Victrix, now called Chester. However, the marshy ground near Chester made it a poor place for moving troops by land. Suetonius may have used an old crossing of the River Dee near Holt, about 13 km south of Chester, to reach the Menai Strait. An army traveling along the north coast of Wales would first see Anglesey from the Sychnant Pass near Abergwyngregyn, where three land routes meet.
The Roman forces had to cross the Menai Strait, a narrow waterway about 8 km long that separates Anglesey from the Welsh mainland. Crossing the strait was easier during slack water, but strong tidal currents could reach 7.5 knots in rocky areas. Planning the crossing required knowledge of the tides. Later, when Agricola invaded Anglesey, the native people were surprised because they had expected a fleet to arrive earlier.
The exact locations of the Menai crossings are unknown, and modern suggestions are guesses. William Manning proposed a site near Bangor, at the northeastern end of the strait, where medieval travelers used the Lavan Sands to cross. At low tide, the sands would allow flat-bottomed boats to be loaded and cavalry to prepare for swimming. A crossing from Bangor Flats would require moving about 1.5 km across tidal sands to reach a 240-meter sea crossing. If Suetonius had camped near Penrhyn Castle, a similar crossing might have been possible. Soldiers would need to time their movements carefully to avoid being caught by the tide before crossing. Both sites would require fighting uphill from the water’s edge, except near Gallows Point, where a flat area exists.
The parish of Llanidan is on Anglesey near the southwestern end of the Menai Strait. Crossing here would involve a longer sea journey, but the currents are gentler, and the slopes are less steep. However, there are no large sand flats on the mainland side, and troops would need to move through high ground or a valley that might have been used for ambushes.
In the 1700s, Henry Rowlands identified a ford at Porthamel in Llanidan, across the Menai Strait from Felinheli, where he believed the Roman cavalry swam and a ritual sacrifice took place.
Local field names in Llanidan, such as "Maes Hir Gad" (Area of long battle) and "Cae Oer Waedd" (Field of cold or bitter lamentation), recorded in 1867, suggest they might mark the site of a Roman attack.
The landing on Anglesey was met by a large group of warriors, Druids, and women. Tacitus wrote that the enemy stood on the shore with armed fighters, while women in black clothing ran between them, waving torches. Druids raised their hands to the sky, chanting curses, which frightened the Roman soldiers so much they stood frozen and exposed to attacks. Roman soldiers were rarely described as being paralyzed by fear, so this event must have been shocking even for experienced soldiers.
Despite the initial fear, the Romans regrouped and won a brutal battle. Tacitus reported that the soldiers, encouraged by their general, pushed forward, defeating the enemy and setting their torches on fire. The Romans destroyed sacred groves and believed it was their duty to cover their altars with the blood of captives and consult their gods through human sacrifices. No sacred groves have been confirmed on Anglesey, but late Iron Age ritual items have been found near Llyn Cerrig Bach on the other side of the island.
The Roman army stayed on Anglesey long enough to begin garrisoning the island but soon received news of a rebellion in southern Britain. Tacitus wrote that Suetonius received word of the sudden revolt and, with great determination, marched through hostile territory to Londinium.
The Roman troops left Anglesey, which remained free from Roman rule for sixteen years until Agricola led the second invasion.
Between Roman attacks
After the Boudican revolt, the Roman conquest of Wales was paused. Between the leaders Suetonius and Agricola, the province of Britannia had five British governors, but none led military campaigns in the area known as Cambria. At this time, the Romans faced challenges across the Empire, including conflicts within the military and unrest among soldiers stationed in Britain. These issues, along with the effects of Boudica's rebellion, led the Romans to avoid expanding their territory in this period. The conquest of Wales was restarted when Vespasian became emperor in 69 CE, as recorded by Tacitus in his book The Life of Gnaeus Julius Agricola. After several governors who did not take active roles, Julius Frontinus arrived in 74 CE to continue the conquest of Wales. Tacitus mentions Frontinus briefly, stating that he defeated the powerful Silures tribe in southern Wales. He also writes: "This was the situation in Britain, and these were the changes in the war that Agricola faced when he arrived around midsummer. Our soldiers used this as an excuse for being careless, thinking the fighting was over and the enemy was waiting."
Second invasion (77 CE)
The second invasion of Anglesey was led by Agricola, who was the Roman Governor of Britannia at that time, in late 77. Tacitus wrote about this invasion, but his account may include exaggerated details. Careful consideration of his reliability is important, as Tacitus was married to Agricola’s daughter. His description is the only written record of the second invasion.
Tacitus suggested that tribes living near the Roman province were generally hostile. They avoided rebellion because of fear of Roman forces and their leaders. These tribes were also aware of events and important people in other parts of Britain. He wrote: "The Ordovices had recently destroyed nearly all of a group of allied cavalry stationed in their land. This action raised hopes among the people, and those who wanted war supported it. They closely watched the new governor’s actions. Meanwhile, Agricola, even though summer had ended and troops were spread across the province, decided to act despite challenges. Many advisors believed it was better to wait and observe weak areas, but Agricola chose to face the danger."
Tacitus described Agricola as a brave and determined leader. He wrote: "Agricola gathered a group of experienced soldiers and a small number of helpers. Since the Ordovices avoided fighting in open areas, Agricola led his troops up a hill to inspire courage. The tribe was nearly destroyed." The battle’s exact location is unknown, but the hillfort Dinas Dinorwig is located on a foothill about 3 kilometers from the Menai Strait. The name "Dinorwig" is thought to mean "fort of the Ordovices."
Tacitus credited Agricola’s success to his leadership skills. He wrote: "Agricola understood that he needed to continue his victories to scare other tribes. He planned to take control of the island of Mona, which had previously been abandoned by Paulinus due to a rebellion. However, he did not yet have a fleet." Agricola’s earlier victory on the mainland allowed him to position his forces near the Menai Strait and the island, which he and some veterans likely remembered.
Tacitus praised Agricola’s military strategy. The attack on Mona was a surprise carried out by local soldiers who swam across the strait without using boats or legionaries. The defenders on Mona had expected more time to prepare, and the sudden attack caused them to surrender. Tacitus wrote: "The general’s skill and bravery made the crossing possible. A group of skilled auxiliaries, carrying no extra supplies, used their knowledge of shallow waters and swimming to reach the island. The enemy, expecting a naval attack, were shocked and believed nothing could stop these attackers."
The location of this crossing is also unknown and could have been anywhere along the Menai Strait. Some place names near Llanidan might be connected to this invasion rather than an earlier one by Paulinus. An army from Dinas Dinorwig could have traveled directly, about 3 kilometers, to the southwestern part of the Menai Strait near Llanidan.
Tacitus highlighted Agricola’s achievements: "After the enemy surrendered, Agricola became well-known and respected for his success."
Aftermath
After the second invasion of Anglesey, the Romans ruled the island for more than 300 years.
The Cemlyn Cropmark is the first known Roman military site on the island, dating to around 77 CE, the time of the second invasion. It was discovered in 1990 on an aerial photograph during a dry period. In 2015, a geophysical survey of the cropmark showed features typical of a Roman fortlet. Partial excavation uncovered two coins, one from the reign of Emperor Nerva and one from Emperor Hadrian, supporting the idea that the fortlet was built after the invasion to help control the area. The fortlet overlooks Cemlyn Bay, a good landing spot on the north coast of the island, and likely served as a guide for ships arriving and as a place to monitor people entering Anglesey.
The Romans managed the island from Segontium (now Caernarfon), a Roman fort in mainland Wales across the Menai Straits. By the end of the Roman period, in most parts of the Empire, local leaders had adopted Roman customs. However, no city has been found on Anglesey, nor any signs of such leaders. Archaeological findings show few buildings with Roman-style designs. At Caer Lêb in the south of the island, there is evidence of a possible farmstead with a few rectangular buildings from the Roman period, but most nearby homes were traditional round houses. This suggests that farming continued with little change after the Roman conquest by Agricola.
Copper had been mined on Parys Mountain for many years before the Romans arrived, and copper production—possibly increased for export—seems to have continued. About 18 round copper ingots, eight with Roman markings, have been found on the island, two on Parys Mountain itself. However, the locations of the smelting sites are unknown.
The settlement at Tai Cochion is near the Menai Strait, across from Segontium, the Roman fort that oversaw the island. Excavation of one building there revealed what appears to be Roman-style corridor housing, unlike the circular huts used elsewhere on the island. Pottery and coins found there date its active period to 100–300 CE, suggesting it was established as a civilian trading center shortly after the second invasion.
For centuries, little changed on the island. However, by the mid-fourth century, a shore-fort called Caer Gybi, facing Ireland, was built to protect the island from sea threats. The fort’s walls are still visible today. Around the same time, Parciau hill fort had a large population in a defensible location, showing that people felt unsafe. Saint Patrick was kidnapped from somewhere near the west coast of Great Britain around 400 CE and taken as a slave to Ireland. His Letter to Coroticus describes a violent slave raid from Great Britain to Ireland.
Pen Bryn-yr-Eglwys is a rocky hilltop on the north-western corner of Anglesey, with a square stone platform measuring 9 meters by 7 meters on top. This has traditionally been thought to be the remains of a chapel. However, the platform’s location, size, and the presence of three pieces of pottery likely from the Roman period strongly suggest it was a Roman watchtower.
A similar site, also believed to be a watchtower, was found inside the pre-Roman fort of Caer y Twr on Holyhead Mountain. There may also be a second fortlet on Bwrdd Arthur, near the eastern end of the north coast of the island.
Direct Roman military control on Anglesey may have ended around 383 CE, when Magnus Maximus took much of the Roman garrison from Britain to the Continent to support his failed attempt to claim imperial power. In 410 CE, Emperor Honorius told the remaining Roman cities in Britain to defend themselves, and no Roman government later sent officials to Britain.
The fort of Caer Gybi in Holyhead is now the site of St Cybi’s Church. According to a 12th-century source, the site was given to Saint Cybi by Maelgwn Gwynedd in the sixth century CE.