Aed Finliath had become High king in…

Constantine and Methodius, to facilitate the task of preaching in the vernacular and translating the Bible into the unwritten Slavic language, invent a script, initially known as Glagolitic, using the phonetic peculiarities of the Slavic tongue.

German leaders, however, want to enforce the use of the Latin liturgy among the Slavs, and the brothers are called to Rome to defend themselves.

After some two and a half years among the Moravians, the two brothers journey to Rome to ask for papal support for their work and their use of the Slavic language.

Constantine enters a convent in Rome, taking the name of Cyril; he will die in 869.

The new alphabet, attributed to Cyril but probably the work of his followers, will subsequently be revised to employ characters resembling those of the Greek to become the Cyrillic alphabet used in modern Slavic languages.

Basil, on Emperor Michael's orders, had divorced his wife Maria and married Eudokia Ingerina, Michael's favorite mistress, in around 865.

During an expedition against the Arabs, Basil had persuaded Michael III that his uncle Bardas covets the imperial throne, and subsequently murders Bardas on April 21, 866, with Michael's approva .

Basil now becomes the leading personality at court and is invested in the now vacant dignity of kaisar (caesar), before being crowned co-emperor on May 26, 866.

This promotion may have included Basil's adoption by Michael III, himself a much younger man.

It is commonly believed that Leo VI, Basil's successor and reputed son, is really the son of Michael.

Although Basil seems to have shared this belief (and hated Leo), the subsequent promotion of Basil to caesar and then co-emperor provides the child with a legitimate and Imperial parent and secures his succession to the imperial throne.

It is notable that when Leo is born on September 19, 866, Michael III celebrates the event with public chariot races, while he pointedly instructs Basil not to presume on his new position as junior emperor.

Boris sends embassies to Pope Nicholas and to Louis the German in 866; the Pope’s immediate response is to send a mission to Bulgaria.

Ya'qub next invades Bamian, …

…Balkh, …

…Badghis, and …

…Ghor.

Conquering these territories, which are ruled mostly by Buddhist tribal chiefs, in the name of Islam, Ya'qub takes vast amounts of plunder and slaves from this campaign.

The Cretan Arabs, despite some imperial successes in the latter half of the 850s against the Emirate of Crete, in the early 860s resume their raids, attacking the Peloponnese, the Cyclades, and Athos.

The Caesar Bardas in 866 assembles another large-scale expeditionary force to subdue Crete, but his murder by Basil the Macedonian only two weeks after the fleet sets sail from the capital spells the end of the undertaking.

Emperor Louis, in his efforts to restore order in Italy as met with considerable success both against Italy's turbulent princes and against the Saracens who are ravaging southern Italy.

He routs these invaders, who have seized Bari, Taranto, and various other places in southern Italy, in 866, but cannot follow up his successes owing to the lack of a fleet.

King Ordoño I of Asturias dies in Oviedo in May 866, marking the end of his 16-year reign. He is succeeded by his eldest son, Alfonso III, who ascends the throne as King of Asturias.

Alfonso III will go on to strengthen the kingdom, expand its territory, and lay the foundations for the future Christian Reconquista, securing his legacy as one of the most important early rulers of Asturias.