Arnulf de Montgomery (born 1066; died 1118/1122) was an Anglo-Norman magnate. He was a younger son of Roger de Montgomery and Mabel de Bellême. Arnulf's father was a leading magnate in Normandy and England, and played an active part in the Anglo-Norman invasion of Wales in the late eleventh century.
Following the Montgomerys' successes against the Welsh, Arnulf established himself at Pembroke, where an earth and timber castle was erected, and was probably rewarded with the title Earl of Pembroke.
At the turn of the twelfth century Arnulf reached height, with his lordship including much of the former Welsh Kingdom of Deheubarth as well as various lands in Yorkshire. Not long after reaching this apex of his career, Arnulf assisted his eldest surviving brother, Robert de Bellême, in a rebellion against Henry I, King of England. It was also about this time that Arnulf married a daughter of Muirchertach Ua Briain, King of Munster, in what appears to have been an effort to gain military support against the English Crown.
Following the ultimate collapse of the rebellion, however, the Montgomerys were outlawed and banished from the realm, and Arnulf appears to have spent much of the next twenty-odd years in a peripatetic life in Ireland and Normandy. Arnulf's career exemplifies the opportunities available to younger sons of the Anglo-Norman aristocracy. Arnulf appears to have died between 1118 and 1122. A tombstone in Tulsk, Ireland bears the name of Arnoul (Arnulf) and the date 1122.
Arnulf and his wife Lafracoth (daughter of Muirchertach Ua Briain, King of Munster) are known to have left one daughter, Alice, who was born circa 1115; however, according to Europäische Stammtafeln, Arnulf and Lafracoth had two children, Robert and Alice, who would have progeny.
Background
thumb|upright|alt=Map of Britain, Ireland, and France|Locations relating to Arnulf's life and times.
Arnulf was likely born in the late 1060s, possibly about 1066. He was a younger son of Roger de Montgomery, Vicomte of the Hièmois and Mabel de Bellême. Arnulf's parents likely married in about 1050. His mother was a daughter of, and eventual heiress of, William de Bellême, Lord of Alençon. As tutor to Matilda, Duchess of Normandy, Roger and his eldest sons did not embark on the 1066 Norman invasion of England. When William returned to Normandy as king in 1067, Roger accompanied him back to England, and was granted extensive lands, including the Sussex rapes of Arundel and Chichester, followed by the county of Shropshire. Arnulf makes his first appearance in the historical record at about this time when he and his elder brother, Roger de Poitou, witnessed William's confirmation of their father's grant to the Norman abbey of Troarn in 1082/1083.
thumb|left|The [[Bayeux Tapestry's depiction of the Battle of Hastings. Although Arnulf's family did not participate in the invasion of England in 1066, it was richly rewarded with English lands soon afterwards.]]
In 1088, Roger and at least three of his sons participated in plot to eject William Rufus, King of England from the throne with the intent to replace him with Robert Curthose, Duke of Normandy, William Rufus' elder brother. This rebellion is documented by several sources, such as the ninth- to twelfth-century Anglo-Saxon Chronicle, and the twelfth-century texts Chronicon ex chronicis, Gesta regum Anglorum, and Historia Anglorum. According to the "E" version of the Anglo-Saxon Chronicle—the only strictly contemporary source of the four—Robert Curthose's followers captured Odo, Bishop of Bayeux and thereby gained control of the castle of Rochester. This source identifies several leading members of the insurrection, including three unnamed sons of Roger. Whilst it is possible that these brothers were Roger's eldest sons Robert de Bellême, Hugh de Montgomery, and Roger de Poitou, it is not impossible that the latter took no part in the rising, and that the third brother was in fact Arnulf himself. Although the rebellion was an ultimate failure, the king imposed no penalty upon Roger, and allowed Roger de Poitou to be reinstated with most of the lands that the eleventh-century Domesday Book shows he previously held.
Rise
upright|right|thumb|Anglo-Norman advance into Wales, and the penetration of Montgomery power into [[Deheubarth, where Arnulf established himself at Pembroke in about 1093.]]
Arnulf's father was one of three close supporters of the king who were settled along the Anglo-Welsh border, in a region known as the Welsh marches. Although the first real penetration of Anglo-Norman power occurred in the 1070s, it wasn't until the last decade of the eleventh century that more permanent marcher settlements were envisaged in Wales. In 1093, encroaching marcher lords engaged and slew Rhys ap Tewdwr, King of Deheubarth in Brycheiniog. Contemporaries marked Rhys' fall as the end of kingship amongst the Welsh, and his demise left a power-vacuum in which men such as Arnulf seized upon. The south-west Welsh ("countries") of Ceredigion and Dyfed were thus overwhelmed and settled by the conquering incomers. This ringwork, strategically seated on the highest point of a promontory between two tidal inlets, sat on the site where the castle of Pembroke stands today. Although nothing now remains of the original castle, it is described by the twelfth-century Itinerarium Kambriæ as a "slender fortress built of stakes and turf".
William Rufus subsequently rewarded Arnulf with a lordship seated at his castle. There is substantial evidence indicating that Arnulf was, in fact, made Earl of Pembroke. For example, he was accorded forms of the Latin style by Anselm, Archbishop of Canterbury, Itinerarium Kambriæ, the twelfth-century Vita Anselmi, the twelfth-century Historia ecclesiastica, the thirteenth- and fourteenth-century Brut y Tywysogyon, the twelfth-century Warenne Chronicle, and the cartulary of the abbey of Saint-Martin de Sées. The castle at Pembroke is remarkable in the fact that, unlike other Anglo-Norman or English fortresses in west Wales, it never fell into the hands of the Welsh. At some time between 1097 and 1108, Arnulf's castellan at Pembroke, Gerald de Windsor, married Rhys' daughter, Nest. According to Brut y Tywysogyon, Arnulf captured and imprisoned Rhys' young son, Hywel, before the latter was able to escape after suffering certain bodily injuries. Having established himself at Pembroke, Arnulf appears to have resided in England, leaving Gerald at Pembroke as his or steward.
On his father's death in 1094, Arnulf's elder brother, Hugh de Montgomery, inherited the earldom of Shrewsbury. Surviving sources reveal that the brothers were closely associated with each other. Within two years they made a joint grant to the far-off abbey of La Sauve-Majeure. Furthermore, Arnulf appears to have witnessed a grant of Hugh de Montgomery's to the abbey, in a charter dated to 1095–1098. In a Latin grant to the abbey of Saint-Martin de Sées, Arnulf bestowed a donation on behalf of his ancestors, lord, friends, and "very dear brother Hugh" (""). Although the particular wording in this grant may reveal genuine affection for his brother, and that William Rufus intended to acknowledge this inheritance as well. Arnulf's fortress was replaced with this stone castle by William Marshal, Earl of Pembroke, and further construction was continued by the latter's heirs and successors.]]
Partly as a result of the political conquest of Wales in the late eleventh century, the Anglo-Norman Church endeavoured to subjugate and exploit the Welsh Church. From the perspective of the English Crown, the Welsh Church was isolated, archaic, deviant, and backward-looking. Conversely, Anglo-Normans regarded themselves as religious reformers, and sought to impose their own standards and practices upon the Welsh. One way in which the Anglo-Normans imposed their ecclesiastical authority upon the Welsh was through the appointment and control of bishops. Within a year of his consecration as Archbishop of Canterbury in December 1093, Anselm temporarily suspended the Welsh bishops of Glamorgan and St Davids, revealing that these diocesan territories had fallen under Canterbury's ecclesiastical authority. In May 1095, Wilfrid, Bishop of St Davids came to terms with Anselm. In turn, the latter admonished several leading Anglo-Normans holding lands in the Diocese of St Davids, urging them to regard Wilfrid as their bishop, and to return the lands, tithes, and churches that they had unjustly seized from him. Two marcher lords specifically singled out by Anselm were Arnulf and Robert de Bellême. In fact, the ravaging of the lands of St Davids in 1097 by Arnulf's steward at Pembroke, Gerald, is recorded by the thirteenth- and fourteenth-century Brenhinedd y Saesson, Brut y Tywysogyon, the "B" and "C" versions of the eleventh- to thirteenth-century Annales Cambriæ. As a friend of the archbishop, Arnulf may have been more liable to respect this call of restraint from Anselm than from anyone else.
left|thumb|alt=Black and white photograph of a mediaeval seal depicting a mounted knight.|[[Seal (emblem)|Seal of William Rufus. The device depicts the armament of a late eleventh-century mounted knight.]]
In 1098, together with Hugh d'Avranches, Earl of Chester, Hugh de Montgomery led a summer invasion of Gwynedd. Although the Anglo-Normans easily defeated the Welsh defenders, the attackers were later overwhelmed on Anglesey in an encounter with the forces of Magnús Óláfsson, King of Norway. Arnulf appears to have learned of his brother's fate about a month later in Normandy, since he travelled to Sées, and founded a priory of the abbey's monks at Pembroke in dedication to the memory of Hugh de Montgomery and his father. Although Arnulf may well have hoped to inherit his brother's title and lands, William Rufus granted them to Arnulf's older brother Robert de Bellême, who had captured Helias de la Flèche, Count of Maine only months before, dutifully handing the count over to the king.
Downfall
right|thumb|alt=Illustration of a seated mediaeval king|William Rufus as depicted on folio 5r of British Library Royal 14 B VI.
At the turn of the twelfth century, the Montgomerys were one of the leading families in England. At this point, Robert de Bellême had reached the height of his power, and appears to have been the most powerful and prosperous magnate in the Anglo-Norman world. Besides inheriting the expansive continental lands of the Montgomery and Bellême families, and succeeding to the earldom of Shrewsbury and the rape of Arundel, Robert de Bellême also obtained the honour of Tickhill in Nottinghamshire and southern Yorkshire. Furthermore, by right of his wife's inheritance, Robert de Bellême gained the small but important continental county of Ponthieu. His brother, Roger the Poitevin, was one of the most powerful magnates in northwest England, holding lands in Lancashire, Nottinghamshire, Essex, Yorkshire, and Suffolk. By right of his wife, he gained the continental county of La Marche. As for their brother, Arnulf, he likely held the Earldom of Pembroke, a lordship which appears to have constituted the core of the former Kingdom of Deheubarth. Arnulf gained the lordship of Holderness, following the downfall of its former lord, the disgraced Odo, Count of Champagne.
left|thumb|alt=Refer to caption|[[Robert Curthose as depicted on folio 5r of British Library Royal 14 B VI. One of the guarantors recorded lending surety for the English king was Arnulf himself. Guarantors to such acts often led negotiations between involved parties, which could indicate that Arnulf acted as an intermediary between the king and count. by the time Robert Curthose asserted his claim to the throne at Alton in 1101, Robert de Bellême was supporting the duke's cause. According to Brut y Tywysogyon, Arnulf was likewise summoned and charged. Arnulf appears to have fled to Wales, and Historia ecclesiastica records that Robert de Bellême fortified his English castles against Henry's men. Whilst Robert de Bellême made alliances with the Welsh, Specifically, Brut y Tywysogyon reveals that Arnulf sent Gerald of Windsor to Ireland in order to arrange military assistance from Muirchertach Ua Briain, King of Munster. The alliance was formalised by a remarkable marriage between Arnulf and one of Muirchertach's daughters, the record of which is preserved by Historia ecclesiastica, Brenhinedd y Saesson, Brut y Tywysogyon, and alluded to by the eleventh- to fourteenth-century Annals of Inisfallen. These sources are further corroborated by a particular letter from Muirchertach to Anselm,—perhaps dating to about 1105 or 1106/1107,—in which Muirchertach expressed his gratitude to the archbishop for intervening with Henry on behalf of "my son-in-law Arnulf". Historia ecclesiastica names her "" in Latin. One possibility is that her name represents . Another is that it represents .
thumb|alt=Refer to caption|right|The name and title of [[Muirchertach Ua Briain as it appears on folio 63r of Oxford Jesus College 111: "".]]
What specifically motivated Muirchertach to agree to an alliance is unknown. It certainly brought him into close contact with one of Europe's leading families. One possibility is that he was attempting to enhance his status on an international stage. He may have also sought to secure the valuable trade route from south Wales and the Bristol Channel to Waterford.