The frescoes, painted by Pietro Cavallini between 1280 to 1300 -- years before the Assisi frescoes attributed to Giotto -- were recently found by a Rome University team restoring a chapel in the church of Santa Maria in Ara Coeli on the Capitoline hill. Most guidebooks say that the Cavallini frescoes were destroyed during the 16th century when the church was being rebuilt. The leader of the Rome U. team, Tommasso Strinati, suspected otherwise, however, and began searching Santa Maria in Ara Coeli early this year for traces of the lost Cavallinis. Thus far, only three splendid Cavallini frescoes have already been identified in a side chapel (the search continues) but they are expected to necessitate drastic revisions of Art History textbooks.
Although Cavallini is under-represented and little known in our time, he was certainly famous and considered the best fresco artist in his own day. Ironically, it was this early fame that caused most of his work to disappear: his frescoes were in all of the most famous churches, and those were the ones which were also most likely to be rebuilt or redecorated in later days. Cavallini's works, thus, were most likely to be demolished or overpainted. His most famous fresco cycles were in St. Paul fuori le Mura, which was destroyed by fire in 1823 (some of his mosaics there survived), and in the old church of St. Peter in the Vatican, which was completely destroyed when the current baroque basilica was built. Until the recent rediscoveries, the only know surviving Cavallini works in Rome were his mosaics in S. Maria in Trastevere and his Last Judgement fresco in S. Cecilia in Trastevere.
Both the newly uncovered frescoes and Cavallini's other known works clearly demonstrate that Cavallini was already using perspective and painting natural (rather than stylized, Byzantine) representation of animate subjects -- humans, angels, animals. The historical record also clearly connects the younger Giotto with Cavallini: some sources go so far as to say Cavallini was Giotto's mentor.
And there's more: two of Rome's art historians and restoration experts, the late great Federico Zeri and Bruno Zanardi, see Cavallini's hand, rather than Giotto's in the Assisi frescoes.
So who made the mistake. Giotto himself never claimed to have invented the new style of representation. He clearly knew what Cavallini and Cimabue (another member of the older generation) were already doing. The error in accreditation seems to rest on the shoulders of the 16th century undistinguished artist but master art historian, Giorgio Vasari. The still standard (but obviously badly flawed) version of the origin of Renaissance art first appeared in the famous 1550 edition of Vasari's Lives of the Great Artists. The misinterpretation was carried forward into the present generation by Kenneth Clark (Civilization) and Ernst Gombrich (The Story of Art). Vasari did not perpetrate a fraud -- he just got it wrong. Clark and Gombrich weren't aware of current scholarship.
The newly uncovered frescoes: http://www.sunday-times.co.uk:80/news/pages/tim/2000/09/28/timfgneur01004.html
Cavallini in Assisi? http://www.prospect-magazine.co.uk/highlights/portrait_pietro/index.html
Cavallini's previously extant works: http://www.kfki.hu/~arthp/html/c/cavallin/index.html
Encyclopedia Britannica bio of Cavallini (which notes his influence on Giotto): http://www.britannica.com/bcom/eb/article/7/0,5716,22237+1+21901,00.html?query=cavallini