One of Simone Martini's first major commissions was his version of the Maestà for the Council Chamber of the Palazzo Publico of Siena:

This painting was apparently completed in 1317. Compare it to Duccio's Maestà:

Also compare Martini's painting to Giotto's Ognissanti Madonna:

Compare the following details from the two works:

One of the major works of Simone Martini is The Annunciation Altarpiece (1333)now in the Uffizi:

I also want to consider Martini's late Passion Altarpiece made for a Cardinal from the Orsini family probably between 1340-44. The work is no longer intact, but individual panels appear in different collections:

Carrying the Cross	Crucifxion
Deposition	Entombment

Useful comparisons of these works can be made to works by Giotto and Duccio.