In this special blog post for Easter Day, Laura Beknazarian, one of our Open Treasure Gallery Attendants, looks back at the various systems that were historically used to calculate the correct day in which to celebrate the Christian festival of Easter.

Easter is one of the oldest Christian holidays. In the early years of Christianity, Easter would be celebrated at Passover, a Jewish holiday which was held on the fourteenth day of Nisan, the first lunar month of the Jewish year.

However, the First Council of Nicaea (325 A.D.) stated that Christians should no longer use the Jewish calendar. Instead, they should universally adopt the practice of celebrating Easter on a Sunday, the day of Christ’s resurrection.

Calculating the correct Sunday to use was a complex process.  As a result, different systems for calculating the date of Easter emerged in different parts of the Christian world.  The confusion over how to choose the right date to celebrate Easter caused particular problems in the 7th century Kingdom of Northumbria. At least three systems were in use.

The Irish/Celtic system of calculating Easter originated in Gaul and was brought to Northumbria by the first missionaries invited from Iona by King Oswiu.  This system is often called the Latercus system by historians and was widely used in the north of Ireland and Britain.  It used an 84-year cycle of Easter dates.

In Rome, meanwhile, there were two rival systems for establishing the date of the Easter festival. The first one was called Victorius. It was devised in the 450s by Victorius Aquitaine. This calendar was introduced to Northumbria by a missonary called Paulinus, who was initially dispatched to Britain by Pope Gregory I in 601 to serve the first Christian king of Kent.

Dionysius Exiguus, a monk who lived in the 6th century, explored the shortcomings of the existing Easter calculations and devised a new set of tables to resolve the problem.  It is not known exactly when his tables came to Northumbria but they were certainly known by the late 7th century.

This image shows Dionysius’s preface to his own Easter Tables. It is a page from an important 12th century medieval manuscript produced at Durham Priory. The manuscript brought together a collection of scientific and medical texts, including works on calendars (Durham Cathedral Library MS Hunter 100 f24v).

Different methods of calculating Easter led to different dates, with discrepancies sometime as much as a month apart.  The clash of calculations caused practical problems in Northumbria.  Bede famously reported that Queen Eanfled was still fasting for Lent while her husband King Oswiu was celebrating Easter.

King Oswiu convened the Synod of Whitby in 664 to resolve this and other issues. This meeting of the most distinguished monks and scholars of the age decided, among other things, which system to follow for dating Easter: Celtic or Roman/Dionysian.

Wilfrid, later a bishop and Saint, had recently returned from Rome and strongly argued for the Roman position. He claimed that those who did not follow the Roman practice were defying Saint Peter and committing a sin.

This page, from the same early 12th century manuscript, shows the beginning of Dionysius’s Paschal tables (Durham Cathedral Library MS Hunter 100 f27v).

King Oswiu had favoured the Celtic usage, but opted at the Synod to support Wilfrid and the Dionysian calendar.

There are different explanations for his decision.  Bede describes one legend, in which the king was told that after his life on Earth he would be greeted at the gates of heaven by St. Peter, holding the keys to God’s kingdom. That image is profoundly linked to the Church of Rome and the papacy.

However, there is a widely held belief that Oswiu was making a smart diplomatic decision to appease both the Irish strand of Christianity that was so influential in converting Northumbria, while still supporting the Pope and the authorities of the church in south of Britain. Although Oswiu rejected the Celtic Latercus tables in favour of the Roman Dionysian system, he did not invalidate the ordination of followers of the old Celtic calendar. He also maintained the episcopal seat at York, closely connected with the supporters of the Victorius calendar.

In fact, his reasons for choosing the Dionysian calendar were much more political than religious, seeking to bring peace and compromise to the squabbling factions of Northumbria’s clergy. His decision also pleased many in Rome as it helped to resolve an on-going dispute among the ‘Romans’ themselves.

Thanks to Wilfrid’s advocacy and the King’s support, the Synod chose to adopt the Dionysian system. Northumbrians would now celebrate Easter together.

Join our special Easter Day digital service at 11.15am, as we celebrate Our Lord’s glorious resurrection with the Bishop of Durham. The service will be broadcast live on the cathedral’s Facebook page. Watch with or without an account at



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