How and when did Easter Sunday Start?

Constantine the Great, or Saint Constantine (among Eastern Orthodox and Byzantine Catholic Christians), was an Illyrian Roman Emperor. He was proclaimed Augustus by his troops in 306 AD, ruled an ever-growing portion of the Roman Empire until his death. Best known for being the first Christian RomanEmperor, the Edict of Milan - issued by his co-emperor Licinius - helped to put an end to institutionalized persecution of Christians in the Empire. So about 310 AD I would say Easter was being celebrated throughout Rome and Europe.