May 21, 427 BC - Greek Philosopher Plato is born. A student of fellow thinker Socrates, he went on to found the Greek Academy, where another famous Greek mind, Aristotle, was schooled. Through his orations and philosophical dialogues, Plato became one of the most influential and studied thinkers in history.
May 22, 337 AD - Roman Emperor Constantine dies. Thought of as the first Christian Emperor by many, he legalized Christianity in the Roman Empire through the Edict of Milan (313 AD) and the Council of Nicaea (325 AD). He was baptized a Christian on his deathbed, and later sainted.
May 25, 15 BC - Julius Caesar Germanicus is born. He was a member of the famous Julio-Claudian dynasty in the early years of the Roman Empire. He was the father of future Roman Emperor Caligula, as well as a celebrated and victorious Roman military commander.
May 27, 366 AD - Roman usurper Procopius is executed. Procopius attempted to declare himself Roman Emperor against Valentinian I on September 28, 365 AD by taking the provinces of Thrace and Bithynia. He was eventually betrayed by his own followers, and executed on the order of co-Emperor Valens.