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Hello, in 1054 Cardinal Humbert went into the Cathedral of Constantinople in his hand as a paper ball, which is a document with a very large seal attached, a deed of excommunication, and he slammed it down onto the altar.

As he swept out of the startled church, the paper legate and his entourage stopped at the door and symbolically shook the solid dust of eastern Christianity from their Catholic boots.

The Pope of Rome had decreed that the patriarch of Constantinople was denied his place in heaven, and soon afterwards the patriarch excommunicated the Pope in return.

It was a culmination of an argument over a single word in the Nicene Creed, and after a thousand years of being one church, so began a permanent schism.

But what were the real underlying reasons behind the split? What were its effects? And why did it take until December 1965 for the excommunications to be finally revoked?

With me to discuss the schism of eastern and western Christianity, a Norman Haasley, professor of medieval history at the University of Lester,

Henrietta Leiser, fellow of St. Peter's College Oxford, and Jonathan Shepherd, editor of Byzantine diplomacy, and of the forthcoming Cambridge history of the Byzantine Empire.

Henrietta Leiser, can we get a sense of the way the church is organized prior to these excommunications in the middle of the century?

How many patriarchs, for instance, were there in the Christian world?

The important thing really is to recognise that there are five patriarchs, so there's Rome, Constantinople, Jerusalem, Antioch and Alexandria, and very much of the system is really concerned with the authority of Rome as opposed to the authority of what's called the Pentarchy, which is the five patriarchs are known as the Pentarchy.

But of course for a lot of the time, some of those seas are under Muslim rule, and so you get more of a focus than you might have expected originally between old Rome, Italian Rome, and Constantinople.

As soon as Constantinople was established by Constantin, was the riff beginning, was it inevitable?

I don't know that it's inevitable, but the tension is indeed always there. There is right from the beginning a sense that there's going to be rivalry.

Rome, of course, has the advantage of having St. Peter, and Constantinople hasn't really got a saint.

They do try very hard to have saint Andrew, but they don't really. So to one extent, they don't start going off on a very good footing.

On the other hand, they aren't assailed by barbarians in the way that Rome is, so they have a strength of tradition that Rome loses, and Rome is much more vulnerable for a lot of the period under discussion and the Constantinople.

So over the five patriarchs, Jerusalem, Antioch, Alexandria, Constantinople, and Rome, and we have the Muslim overlay because they rise a Muslim power in the 7th, early 8th century, and they're taking over particularly up.

Are they tolerating these patriarchies, the Muslims at that time?

There's a lot of, I mean there's much more toleration overall than one might think, and I think it's also very important to recognize throughout the period that we're talking about that are Latins in Constantinople.

And equally, of course, a lot of Greeks in Italy, and we shouldn't, and that also Muslims in Italy, in Sicily particularly.

And so the whole thing is much more fluid. I think we now, we tend to think already that there is an east-west divide in ways that there simply isn't, there isn't politically, and there isn't ecclesiastically.

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