The signature of Byrhtferth appears on only two unpublished works, his Latin and Old English Manual, and Latin Preface.

He had also composed a Latin life of St. Egwin, compiled a chronicle of Northumbrian history in the 990's, had written wrote a Latin life of Oswald of Worcester (the Vita Oswaldi) about the year 1000, and it is suggested that he is responsible for the early sections of the Historia regum, or History of the Kings, attributed to Simeon of Durham.

This last attribution is based on the similarity of the style between Simeon and Byrhtferth.

The last of Byrhtferth's works is an unsigned fragment of Old English text on computus in the Manuscript BL Cotton Caligula A.xv, fols. MS 142v-143r, attributed to him because of the stylistic similarity to the Old English that he wrote in Manual.

Byrhtferth has also been credited with Latin commentaries on Bede's De natura rerum and De temporum ratione (first attributed to him by John Herwagen) and a Vita S. Dunstani signed "B" (first attributed to him by Jean Mabillon).

However, many scholars argue that these works were not written by Byrhtferth, but instead were a compilation of material by several writers in the late ninth and early tenth centuries.

This is argued because of the smooth, polished style of these works in comparison with the styles of the only signed works Manual and Preface.

St. John's College, Oxford MS 17, contains several computistical works by Bede and Helperic, and a computus which includes the Latin Epilogus, or Preface, by Byrhtferth.

He also constructed a full-page diagram showing the harmony of the universe, and suggesting correspondences among cosmological, numerological, and physiological aspects of the world.

Other items in the manuscript may in fact be Byrhtferth, but it cannot be proved.

Also, he may have compiled most of these things from works that Abbo of Fleury left behind at Ramsey Abbey after his death.

Bodl. Ashmole MS 328 preserves Byrhtferth's Latin Enchiridion, or Manual.

It is written in Latin and Old English and the largest part is that of a computus similar to the one in Preface.

It touches on the belief that the divine order of the universe can be perceived through the study of numbers and can be of great reference for the study of medieval number symbolism.

It also contains treatises on rhetorical and grammatical subjects, a table of weights and measures and three theological tracts on the ages of the world, the loosing of Satan and the eight capital sins.

Geoffrey de Mandeville II had succeeded his father, William, sometime before 1129, possibly as early as 1116, when a key portion of the family patrimony was in the King's hands.

William had incurred a debt to the crown, perhaps in part due to a large fine levied by Henry I due to his displeasure at the escape of an important political prisoner when William was in charge of the Tower of London.

The King had also held the substantial estate of Geoffrey's maternal grandfather Eudo le Dapifer to which Geoffrey has laid claim.

Geoffrey's goal seems to have been to recover these lost lands and his father's offices.

He had succeeded in this during the shifting tides of fortunes of the two competitors for the English throne after King Henry I's death in 1135.

He had started out supporting Stephen, who sometime in 1140 (most likely May of that year) made him Earl of Essex.

Stephen had by 1140 or 1141 returned to him the lucrative manors in Essex.

The new earl in 1141 had also been appointed custodian of the Tower of London by Empress Matilda.

He had founded a Benedictine priory (later Walden Abbey) at Walden, Essex and has constructed a castle there.

He has also contributed to Hurley Priory in Berkshire, which had been founded by his grandfather Geoffrey de Mandeville I.

After the defeat and capture of Stephen at Lincoln early in 1141, the Earl, like many barons, had acknowledged Stephen's rival Matilda as his sovereign lady.

She had confirmed his custody of the Tower, forgiven the large debts his father had incurred to the crown, granted him the Norman lands of Eudo le Dapifer, and appointed him Sheriff of Essex and Hertfordshire, Middlesex and London.

But before the end of the year, when Stephen was released, he had returned to his original allegiance.

The earl was arrested by the King in 1143 and, threatened by execution, Geoffrey had surrendered his castles to Stephen.

In reaction, the earl launched a rebellion.

Earl Geoffrey maintains himself in 1143-1144 as a rebel and a bandit in the fen-country, using the Isle of Ely and Ramsey Abbey as his headquarters.

Besieged by King Stephen, he meets his death in September 1144 in consequence of an arrow wound received in a skirmish.

Because he had died excommunicate, his body is denied burial.

Wrapped in lead, it is taken by the Templar community in London, where he is buried in the Temple Church in London.

His son, Geoffrey III, arranges for an effigy to be placed on the floor, where it can still be seen today.

The charters Geoffrey had received from King Stephen and Empress Matilda illustrate the ambitions of English barons.

The most important concessions are grants of offices and jurisdictions, which had the effect of making Mandeville almost a viceroy with full powers in Essex, Middlesex and London, and Hertfordshire—but these were based on offices and jurisdictions his ancestors had held.

His career as an outlaw exemplifies the worst excesses of the civil wars of 1140-1147, and it is possible that the deeds of Mandeville inspired the rhetorical description of this period in the Peterborough Chronicle, when "men said openly that Christ and his saints were asleep."

He had seized Ramsey Abbey (near Peterborough) in 1143, expelling the monks and using Ramsey as a base for forays into the surrounding region.