Dendle links this to the fact that while Christianity was already established in most of England, the northeastern region had only recently been converted (England map).
Lasting no more than 50 years, the outbreak may reflect the tension between Christianity and lingering pagan beliefs, Dendle pointed out. Or the spate could have resulted from differences in the way converts understood their new religion.
Afterward, though, "there is no reference to a contemporary Anglo-Saxon case of possession for 300 years," Dendle said.
Anglo-Saxon sources indicate that the English were both puzzled and surprised by cases of possession mentioned both in the Scriptures and European texts from regions such as modern-day France and Germany.
But after the Norman Conquest, possession stories and exorcisms quickly appear in England, Dendle found.
These reports coincided with growing use of healing shrines and pilgrimage routes by people in search of miracle cures, the researcher suggests.
Christina Lee of the University of Nottingham in England says saintly relics that supposedly had healing properties were increasingly advertised by monasteries and churches as cures for the possessed or the mad.
"There were churches vying to have the most powerful saint, while monasteries had hospitals attached to them," Lee said. "They saw themselves as doctors of the soul."
One argument is that demon possession as a religious concept was good for business.
If cures appeared to work, "people would be very grateful and leave donations—which the churches and monasteries were dependent on," Lee pointed out.
In a forthcoming book, Demon Possession in Anglo-Saxon England, English professor Dendle draws parallels between the phenomenon in medieval England and its resurgence in the West in recent decades.
The author notes, for instance, that a widespread increase in possessions and exorcisms in America were sparked in part by the 1973 horror movie The Exorcist.
This shows how culture can affect such practices and how "attitudes toward the demonic can radically shift in a very short period of time," he said.
"Demon possession as a living social phenomenon has made a 'miraculous' comeback over the last 30 years," Dendle added. "It's currently a growth industry in America and England as well as throughout the developing world."
Such a trend is seen today mainly among Evangelical Christians, such as those belonging to the Pentecostal movement.
Rather than an abstract idea, evil is seen by believers as an actual force that can be manifest when the devil "possesses" someone.
"There is little out there more spectacular than demon possession, and it brings with it an intoxicating aura of mystery and primordial danger—of cosmic forces locked in epic combat," Dendle said.
"I believe this trend will continue to gain momentum for some time."
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