The Anarchy
After Henry I's death in 1135, the throne of England was seized by Stephen of Blois, a grandson of William I of England. Henry's daughter, Empress Matilda (Maud), also claimed the throne, and had the support of the Marcher Lords. On the death of her husband, the Holy Roman Emperor, Henry V, in 1125, Matilda had returned to England for the first time in 16 years. At the insistence of her father, the barons (including Stephen) swore to uphold Matilda's rights as his heir. Matilda married Geoffrey of Anjou in 1128. They lived together in France, having three sons; the eldest of whom was to become King Henry II of England. Initially, Miles supported Stephen. In about 1136, Stephen granted Sibyl's husband the entire honour of Gloucester and Brecknock, and appointed him Constable of Gloucester Castle, whereby Miles became known as one of Stephen's "henchmen". Miles received Stephen at Gloucester in May 1138 and participated in his the kings' siege of Shrewsbury.
Llanthony Priory had been established near Crucorney, in the Vale of Ewyas, in 1118; Wales' earliest Augustine monastery. Miles' father, Walter de Gloucester, had retired there by 1126. The unrest that had been simmering in Wales during the last years of Henry's reign, boiled over in 1135 on his death. The area around the priory returned to Welsh rule, coming under such “hostile molestation” from the Welsh that the non-Welsh canons decided to leave. Miles established a new Priory for them in Gloucester, England, which they called Llanthony Secunda, in 1136. Sometime after 1137, Sibyl, together with her husband, made a further endowment to Llanthony Secunda.
Miles transferred his allegiance to Empress Matilda, on her return to England in 1139. According to Professor Edmund King, Miles' decision to support Matilda was guided by expediancy rather than principle, and the necessity of joining forces with Matilda's illegitimate half-brother, the powerful Robert, Earl of Gloucester, who was the overlord of some of Miles' fiefs. Stephen stripped Miles of the title 'Constable of England' in punishment for having deserted him. On 25 July 1141, in gratitude for his support and military assistance and, according to historian R.H.C. Davis, possibly to compensate Miles for having appeared to have lost the constableship, Matilda invested him as 1st Earl of Hereford. He also received St. Briavels Castle and the Forest of Dean. At the time Matilda was the de facto ruler of England, Stephen having been imprisoned at Bristol following his capture the previous February after the Battle of Lincoln. Sibyl was styled Countess of Hereford, until Miles' unexpected death over two years later. In 1141, Miles received the honour of Abergavenny from Brien FitzCount, the (likely illegitimate) son of Duke Alan IV of Brittany. This was in appreciation of the skilled military tactics Miles had deployed which had spared Brien's castle of Wallingford during King Stephen's besiegement in 1139/1140. Matilda gave her permission for the transfer.
During the Anarchy, which the period of Stephen's reign as King of England was to become known, life was greatly disrupted in her husband's lands. Sibyl would have doubtless suffered as a result, especially after Miles' decision to support Matilda's claim to the throne and to oppose Stephen. When Matilda was defeated at Winchester in late 1141, Miles was compelled to return to Gloucester in disgrace: "weary, half-naked and alone". In November of that same year, Stephen was released from prison and restored to the English throne.
Sibyl's distress would have been heightened in 1143 after the Bishop of Hereford, Robert de Bethune placed an interdict upon Hereford, blocked all the cathedral's entrances with thorns, and excommunicated Miles. In order to raise money to pay his troops and to assist Matilda financially, Miles had imposed a levy on all the churches in his earldom, an act which the bishop had regarded as unlawful. When the bishop protested and threatened Miles with excommunication, Miles in response, sent his men to plunder the diocese of its resources. In retaliation against Miles' earlier attacks on the royalist city of Worcester and the castles of Hereford and Wallingford, King Stephen bestowed the title "Earl of Hereford" on Robert de Beaumont, 2nd Earl of Leicester; Miles, however, never surrendered the earldom nor the title to Robert de Beaumont.
