The high altar is from the 17th century, by the florentine A. Burini and represents, with a splendid inlay of mother of pearl and precious marble, the "Last Supper". The altar piece represents a "Sacra Conversazione" begun in 1520 by Marco Pensaben and completed by Girolamo Savoldo.
To the left of the altar is the monumental "Onigo" tomb, a renaissance work embellished by a tapestry fresco and two army pages, attribuited to Lorenzo Lotto (though other critics attribuite it to Pier Maria Pennacchi).
In the chapel, to the right of the main altar, is a work attribuited for a long time to Lorenzo Lotto: the "Incredulity of St. Thomas" (circa 1505); the altar piece has a lower strip depicting the Commissaria Monigo, a foundation which provided  dowries for poor girls.
In the nave to the right stands an organ, built by Callido in the second of the 18th century; its particular sound is optimised by the church's excellent acoustics, making it a great venue for concerts. To the right of the organ is a giant fresco of St. Cristopher, by Antonio da Treviso in 1410: it is said that the fish depicted at the feet of the Saint are those of the nearby Sile river.
The chapter house of the Dominicans is found in the church's cloister and has frescoes by Tomaso da Modena of 1352: it is one of the most important series of frescoes of 14th century Italy.

The Dominican series in San Nicolò

In 1352, Tomaso da Modena was commissioned by the Dominicans who then resided in the convent of San Nicolò, to beautify the chapter house with images of the 40 dominican monks who through time had honoured the Order, distinguishing themselves in wisdom and holiness.
There were already some frescoes on the walls in the chapter house. These, Tomaso da Modena covered, with new plaster and his own painting. He left only the existing fresco of the Crucifixion intact, and orientated his 40 monks towards this image.
Each monk is depicted in equal cells. Despite this repetitiveness there is no monotony, each figure caught in a different and spontaneous pose: reading, with and expression of amazement, caught in his own thought; writing; correcting what was written; young; old; thin; fat. The artist's models must surely have been the monks staying at the convent.
The ultimate confirmation of the artist's realism and the great attention he paid to reality is found in the image of Cardinal Ugo da Provenza, particulary his eye-glasses: it was the first time in the history of art that eye-glasses were painted. Thus, San Nicolò provides this first piece of evidence.

SANTA CATERINA (ST. CATHERINE)   

In 1312, the Trevisans decide to totally demolished the palazzo of the Caminesi, found in the district of St. Agostino, which had already been ransacked and partly demolished in 1312, when Guecello da Camino had tried to give the City to Cangrande della Scala.
This demolition left a vast tract of empty land, near the urban slum which here encircled the City and in 1346, the Servi di Maria (Servants of Mary) began building the Church and Convent of Santa Caterina.   
The Cappella degli Innocenti which was probably part of the old palace which stood here, also became part of this group of buildings.   
Work continued for many decades with pauses and interruptions. In one of the Church's frescoes, attributed to Tomaso da Modena and dated around 1358, Santa Caterina holds a model of the City in her hands. In the fresco, her words are clearly legible: she is saying, in Latin, that what she is holding in her hands is the City of Treviso on whose behalf she will pray to her God. Amongst the buildings in this fresco, the  unfinished facade the church dedicated to her stands out. It is presumed that the construction of at least its fundamental structure is of 1399, after which it was enlarged and finished in the 15th century.
In 1511, during the war of the Collegati di Cambrai, the main apse was destroyed. It was subject to alterations and radical "restoration" works around 1590. The frescoes were probably whitewashed at this time and remained under lime until 1944.
In 1772, the monks abandoned the convent. During the napoleonic period the Church was completely transformed and reduced to warehouse, military offices and housing, after which it was never again consecrated and no monastic Order ever returned to it.
Now there is the Museum of Santa Caterina. Inside,  some lovely  frescoes of the Storie di S. Orsola (Tales of St. Orsola) painted by Tomaso da Modena are preserved. On the left internal walls, there are also several frescoes from the 14th and 15th centuries, amongst which the "Le Storie di Sant'Egidio), attribuited to Pisanello.
Now the Museum also houses an excursus of the best work from the archaeology section, the picture gallery and the municipal modern art gallery of the Luigi Bailo Musuem, currently being restore.

Tales of Santa Orsola

A few years after the Dominican Series, Tomaso da Modena worked in the chapel of the Church of St. Margherita, painting the fresco Tales of Santa Orsola. Unfortunately, these are no longer there, as the Church was ordered to be demolished, towards the end of last century, and the frescoes were taken and brought to the Civic Museum and thence to Santa Caterina.
The legend of St. Orsola was widely spread in that period: Orsola, a Christian princess, was asked for in marriage by the pagan Prince of England. After a pilgrimage to the Pope in Rome before the wedding, she was martyred by the King of the Huns (who wanted to marry her but was refused) in Cologne, together with her 11,000 handmaidens and the Pope who had accompanied her. This work of art is also animated by realism, in particular the dynamic quality of the Pope's procession and martyrdom scene.
Another, totally new concept in the history of art is found in the scene of Orsola's dialogue with her mother: from the mouth of the Saint come the words which she is saying, just like in modern day cartoons.