St Cissa was a converted pagan who succeeded St Guthlac. This succession was
foretold by Guthlac as recounted by Saint Guthlac's biographer, Felix of
Crowland:
XVIII Concerning abbess Ecgburh.
It happened also on a time that the venerable maid Ecgburh, abbess, the
daughter of Aldwulf the king, sent to the venerable man Guthlac a leaden
coffin, and winding-sheet thereto, and besought him by the holy name of the
celestial King, that after his departure they should place his body therein.
She sent the message by a brother of worthy life, and bid him ask him, who
should be the keeper of the place after him. When he had kindly received the
message of the venerable maid, then concerning that which he was asked - who
should be the keeper of the place after him, - he answered and said, that
the man was of heathen race, and was not yet baptised; but notwithstanding,
that he should soon come, and should receive the rites of baptism. And so it
came to pass ; for the same Cissa, who afterwards held the place, came to
Britain a little time afterwards, and they baptised him there, as the man of
God foretold.
The complete text of the Anglo-Saxon version of Felix's Life of St Guthlac
can be downloaded at google books. Cissa acted as one of the biographer's
sources.
http://tinyurl.com/3lzx69
Cissa is also mentioned in the account of a later ecclesiastical historian
of Crowland:
There were also at that time in the same island, some living the life of
hermits, who, cleaving with holy intimacy to the man of God, as long as he
lived, as the weak cling to the physician, kept their souls continually in a
healthy state by means of his instruction and example. One of these, Cissa
by name, was a recent convert to the catholic faith. He was a man of noble
birth, and formerly exercised great influence inworldly affairs; but he left
all and followed his Lord Christ.
The History of Ingulf in Joseph Stevenson, The Church Historians of England,
Vol 2 (London, 1854), p.572. This work can also be downloaded from google
books:
http://tinyurl.com/3k8cfv
Ingulf's history goes on to describe on p.598 that Cissa's tomb was one of
those adjoining his holy master Guthlac's which was destroyed by the Danes.
Thacker and Sharpe in their book, Local Saints and Local Churches in the
Early Medieval West, (Oxford, 2002), p.521 say that Cissa's relics now rest
at Thorney Abbey in Cambridgeshire, presumably translated there by Bishop
AEthelwold.