Ely Diocesan Coat of Arms
The Diocese of Ely Coat of Arms features 'Gules three crowns or' - the word 'or' in this context means 'gold'. Two are placed above a third, all on a red (gules) background.
The crowns are said to represent the crowns of Etheldreda the foundress, her elder sister Sexburga, who founded the Nunnery at Sheppey and her niece Ermenilda, who succeeded her as Abbesses of the Ely Monastery. All three were queens, which explains the use of the crowns.
Etheldreda was married to Ecgfrith who became King of Northumbria, Sexburga was married to King Erconbert of Kent and Ermenilda to Wulfhere, King of Mercia.
Nicholas Rogers: The Origins of English Diocesan Coats-of-Arms, Harlaxton Proceedings 1998, published 2003: "The earliest English diocesan coat-of-arms, it is generally agreed, is that of Ely: gules three crowns or. The seal of William de Luda (1290-98) is usually cited as its earliest occurrence"
It is possible that the same shield under the feet of the figure of Hugh of Balsham on the first seal of Peterhouse (dated to 1284) may be a slightly earlier example.
There is also a theory that the three crowns are ducal coronets, derived from the arms of the East Anglian Kings.
The Deanery of Ely Crest
"Gules three keys erect or, wards to the dexter"
Meaning three gold (or) keys on a red (gules) background, each standing upright with the end/prongs (wards) of the key pointing to the right hand side of the shield (dexter). [the right hand side from the perspective of whoever holds the shield]
These Arms were originally used by the Priors of Ely, although the background was then gold with three blue keys.
Following the Reformation when the Priors became Deans, the Arms have represented the Dean and Deanery of Ely.
There is much debate about their origins and when they were first used. It is possible that one of the priors began to use the three keys as an unofficial coat of arms.
C. W. Stubbs, Ely Cathedral Handbook 1906, says that the three keys were the arms of Ethelwold, Bishop of Winchester (912-984) who was instrumental in refounding Ely as a Benedictine Monastery in 970.
As heraldry did not become established until nearly 200 years later, these arms were attributed to him at a much later date and could then have been assumed by the Monastery.
With thanks to Chloe Cockerill, 2016, for providing this information.