Q: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
What characteristic set Pietro's paintings aside from other artists back in the great period of Roman mosaic art?, Context: The last great period of Roman mosaic art was the 12th–13th century when Rome developed its own distinctive artistic style, free from the strict rules of eastern tradition and with a more realistic portrayal of figures in the space. Well-known works of this period are the floral mosaics of the Basilica di San Clemente, the façade of Santa Maria in Trastevere and San Paolo fuori le Mura. The beautiful apse mosaic of Santa Maria in Trastevere (1140) depicts Christ and Mary sitting next to each other on the heavenly throne, the first example of this iconographic scheme. A similar mosaic, the Coronation of the Virgin, decorates the apse of Santa Maria Maggiore. It is a work of Jacopo Torriti from 1295. The mosaics of Torriti and Jacopo da Camerino in the apse of San Giovanni in Laterano from 1288–94 were thoroughly restored in 1884. The apse mosaic of San Crisogono is attributed to Pietro Cavallini, the greatest Roman painter of the 13th century. Six scenes from the life of Mary in Santa Maria in Trastevere were also executed by Cavallini in 1290. These mosaics are praised for their realistic portrayal and attempts of perspective. There is an interesting mosaic medaillon from 1210 above the gate of the church of San Tommaso in Formis showing Christ enthroned between a white and a black slave. The church belonged to the Order of the Trinitarians which was devoted to ransoming Christian slaves.
A:
their realistic portrayal and attempts of perspective