Æthelfrith, king of Bernicia, gains control of Deira around 604; the circumstances of this are unknown.

That he gained Deira through conquest is suggested by the exile of Edwin, son of the former king Ælla, and Hereric, Edwin's nephew, who are both notable members of the Deiran royal line; the short five-year reign of Aethelric of Deira, who ruled immediately prior to Æthelfrith's acquisition of Deira, may also indicate conquest.

D. P. Kirby on the other hand suggested that Æthelfrith's rule of both kingdoms may have represented "a formalization of an existing relationship" of cooperation between the two.

Kirby also pointed out that Edwin did not necessarily go into exile immediately, and considered it likely that Æthelfrith's hostility towards him "manifested itself only by degrees".

It is also around 604 that Æthelfrith's son Oswald is born.

Oswald's mother is Acha, daughter of Ælla, and thus Edwin's sister.

Although Bede does not explicitly say Æthelfrith married Acha, it is thought that he did so; he may have married her prior to taking power in Deira, in which case the marriage may have facilitated it, or he may have done so afterwards in order to consolidate his position there.

Mediterranean Southwest Europe (616–627 CE): Ecclesiastical Turmoil, Papal Reforms, and Missionary Influence

The era 616–627 CE in Mediterranean Southwest Europe is marked by ecclesiastical instability, papal reforms, and significant missionary activity extending from Rome to England, set against a backdrop of continued political unrest and external threats.

Ecclesiastical Turmoil and Papal Succession

In August 618 CE, Rome suffers a damaging earthquake, followed closely by an outbreak of a scab disease that claims the life of Pope Adeodatus I (Deusdedit). Adeodatus, a Roman priest elected pope in 615—the first priest elevated to the papacy since John II in 533—had notably reversed some Gregorian practices by restoring clerical administrators over monks in papal administration. Tradition also credits Adeodatus with introducing the use of lead seals (bullae) for papal documents, the earliest surviving example of which prominently depicts Christ as the Good Shepherd.

Following Adeodatus’s death, a prolonged papal vacancy of one year, one month, and sixteen days occurs amidst regional disturbances. Eventually, a Neapolitan is consecrated as Pope Boniface V (r. 619–625 CE).

Rebellion of Eleutherius and Political Instability

Prior to Boniface V’s consecration, Italy endures significant upheaval caused by the rebellion of Eleutherius, the eunuch Exarch of Ravenna. Eleutherius advances toward Rome, aiming to seize power, but is slain by his own troops before reaching the city. The incident underscores ongoing tensions and instability within the Byzantine administration in Italy, complicating ecclesiastical governance.

Papal Reforms under Boniface V

Pope Boniface V, remembered in the Liber Pontificalis as "the mildest of men," introduces key ecclesiastical reforms. He enacts measures clarifying rights of sanctuary, directs ecclesiastical notaries to adhere strictly to imperial laws regarding wills, and regulates the duties of acolytes, forbidding them from translating relics of martyrs or assuming deacon’s roles in baptismal ceremonies at the Basilica di San Giovanni in Laterano. Boniface also oversees the completion and consecration of the cemetery of Saint Nicomedes along Rome’s Via Nomentana.

Missionary Efforts and English Connections

Pope Boniface V notably fosters missionary enterprise, especially directed toward England. According to the Venerable Bede, Boniface V sends affectionate letters to the English Church, including exhortations to Mellitus, Archbishop of Canterbury, and Justus, Bishop of Rochester, although these letters are now lost. A surviving letter from Boniface to Justus, upon his elevation as Archbishop of Canterbury in 624, grants the pallium and authorizes him to ordain additional bishops as necessary.

Bede further records Boniface's letters encouraging King Edwin of Northumbria in 625 to embrace Christianity and to Queen Æthelburg of Kent, urging her to persuade her husband toward conversion. Pope Boniface V dies in October 625 and is interred in St. Peter’s Basilica.

Pontificate of Honorius and Liturgical Development

Following Boniface, Pope Honorius I (r. 625–638 CE), a Campanian by birth and son of the consul Petronius, ascends to the papacy. Honorius’s reign witnesses further ecclesiastical and missionary activity, particularly toward England, notably Wessex. He successfully aligns the Irish Easter celebrations with the broader Catholic Church and institutes the festival of the Elevation of the Cross, a key liturgical observance.

Cultural and Ecclesiastical Continuity

Despite political instability, the Church remains a resilient force of continuity and stability. Papal initiatives continue shaping liturgical practices and missionary outreach, influencing ecclesiastical structures across Europe, particularly in emerging Christian communities such as those in Anglo-Saxon England.

Legacy of the Era

The era 616–627 CE highlights the resilience and adaptability of the papacy in response to both internal ecclesiastical challenges and external political pressures. Papal reforms and missionary activities significantly shape the religious and cultural landscapes of both Italy and distant regions like England, reinforcing the spiritual authority and cultural influence of Rome in early medieval Europe.

The Venerable Bede will writes of Pope Boniface' Vs affectionate concern for the English Church.

The "letters of exhortation" which he is said to have addressed to Mellitus, Archbishop of Canterbury, and to Justus, Bishop of Rochester, are no longer extant, but certain other letters of his have been preserved.

One is written to Justus after he had succeeded Mellitus as Archbishop of Canterbury in 624, conferring the pallium upon him and directing him to "ordain bishops as occasion should require."

According to Bede, Pope Boniface also sent letters to King Edwin of Northumbria in 625 urging him to embrace the Christian faith, and to the Christian Princess Æthelburg of Kent, Edwin's spouse, exhorting her to use her best endeavors for the conversion of her consort.

He is buried in St. Peter's Basilica on October 625.

Pope Adeodatus I represents the second wave of anti-Gregorian challenge to the papacy, the first being that of Sabinian.

He had reversed the practice of his predecessor Boniface IV of filling the papal administrative ranks with monks by recalling the clergy to such positions and by ordaining some fourteen priests, the first ordinations in Rome since Pope Gregory.

According to tradition, he was the first pope to use lead seals (bullae) on papal documents, which in time came to be called "papal bulls".

One bulla dating from his reign is still preserved, the obverse of which represents the Good Shepherd in the midst of His sheep, with the letters Alpha and Omega underneath, while the reverse bears the inscription: Deusdedit Papæ.

Born in Rome, the son of a subdeacon, Adeodatus had served as a priest for forty years before his election in 615 and is the first priest to be elected pope since John II in 533.

Edwin, installed on Æthelfrith’s vacant throne by Raedwald, becomes king not just of Deira but of Bernicia as well.

His reign marks the domination of Northumbria as leading Anglo-Saxon state of the British Isles.

Edwin of Northumbria invades and annexes the minor British kingdom of Elmet in 616 (or 626).

The Deiran exile Hereric had been poisoned while at the court of Ceretic, king of Elmet; Æthelfrith may have been responsible for this killing.

Edwin, apparently seeking safety from Æthelfrith, seems to have traveled between many different kingdoms during his period of exile.

He may have spent time during his exile in the British kingdom of Gwynedd, and it seems clear that he spent time in Mercia, because he married a daughter of king Cearl.

Edwin ended up in East Anglia, under the protection of its king, Raedwald.

Æthelfrith had sent messengers to bribe Raedwald with "a great sum of money" into killing Edwin; Bede reports that his first message had no effect, but Æthelfrith had sent more messengers and threatened war if Raedwald did not comply (bribes and threats of this kind may have previously been used to accomplish Hereric's killing.)

Raedwald had eventually agreed to kill Edwin or hand him over to Æthelfrith's messengers, but was reportedly dissuaded from this by his wife, who said that such a thing was unworthy of his honor.

Instead, Raedwald raises an army and marches against Æthelfrith, and around 616 Æthelfrith is defeated and killed on the east side of the River Idle by an army under Raedwald; Bede says that Æthelfrith had the inferior army, because Raedwald had not given him time to bring all his forces together.

While presented by Bede as being fought simply over the issue of Edwin, this war may have actually involved questions of power and territory between the two rulers.

Æthelfrith's heir, prince Eanfrith, seeks refuge with his mother's family, probably in Gododdin (modern Scotland) and moves further north into Pictland.

Æthelfrith's younger sons Oswald and Oswiu escape to the court of king Eochaid Buide of Dál Riata, where they are soon converted to Christianity by the monks of Iona.

The Angles under Edwin of Northumbria invade Rheged ("Old North") in Northern England and expel king Llywarch Hen.

He flees to Powys and becomes a famous bard.

Edwin's armies fight also against Gododdin and Strathclyde.

King Edwin marries Æthelburga of Kent, who, as a Christian, brings her personal chaplain, Paulinus, and encourages her husband to convert to Christianity.

Edwin defeats the West Saxons under Cynegils, who has tried to thwart the growing strength of Edwin by having him assassinated.

Edwin obliges Cynegils to acknowledge Northumbria's supremacy.