527:

Justinian created co-emperor with Justin

Justinian was the nephew of the Emperor of the Eastern Roman empire, and with the help of his ambitious wife Theodora, he gained the trust of his uncle and was named co-emperor barely 4 months before the older man died.

1081:

Alexius Comnenus crowned emperor

Alexius seized the throne from Nicephorus III. During his reign, he would succeed in reviving the Eastern Roman Empire after half a century of ineffective rule.

1147:

Moscow founded

Although archaeological evidence reveals a settlement has existed on the site of the city of Moscow since prehistoric times, the first documentary reference appears in monastic chronicles concerning this year and date, when a great banquet was thrown. Thus, April 4th has become the traditional anniversary of the founding of the town, which quickly developed into a city of considerable significance.

397:

St. Ambrose

636:

St. Isidore of Seville

896:

Formosus

Although he had an eventful pontificate, Formosus is best known as the subject of the "Cadaver Synod," in which his corpse was exhumed by Pope Stephen VI, propped up on a throne, and subjected to a trial. His election was declared invalid and all his acts were quashed. Stephen's bizzarre synod was later condemned by Pope John IX, and Pope Theodore II reinstated the ordinations of Formosus and had his body reburied.