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The famous recurrent nova (RN) T Coronae Borealis (T CrB) has had observederuptions peaking at a visual magnitude of 2.0 in the years 1866 and 1946,while a third eruption is now expected for the year 2024.4+-0.3. Each RN hasvery similar light curves of eruptions that come with a fairly even-spacing intime, for which T CrB has a recurrence timescale near 80 years. So it isreasonable to look backwards in time for prior eruptions, around 1786, and soon back. I have investigated two long-lost suggestions that T CrB was seen ineruption in the years 1217 and 1787. (1) In a catalog published in 1789, theReverend Francis Wollaston reports an astrometric position for a star that isexactly on top of T CrB. From his letters, these observations were made on atleast four occassions with both a large and small telescope, within a few daysbefore 1787 December 28. Wollaston's limiting magnitude for his astrometry isnear 7.8 mag, so T CrB would have to have been in eruption. With othertransients strongly rejected, the only way that Wollaston could get thecoordinates was to have measured the coordinates of T CrB itself during aneruption. (2) The 1217 event has an eyewitness report written by AbbottBurchard of Upsberg as a fast-rising stellar point-source ("stella") in CoronaBorealis that "shone with great light", lasted for "many days", and wasascribed as being a "wonderful sign". This event cannot be a report of a comet,because Burchard used the term for a star ("stella") and not for a comet, andbecause Burchard had the omen being very positive, with such being impossiblefor comets that are universally the worst of omens. The reported event is justas expected for a prior eruption of T CrB, and all other possibilities arestrongly rejected, so the case for the 1217 eruption of T CrB is strong.

The recurrent nova T CrB had prior eruptions observed near December 1787 and October 1217 AD