From 1400-01, Taddeo worked at the Palazzo Pubblico in Siena where he created twelve small panels, of which only nine exist today, displayed at the Opera of the Duomo in Siena. These panels give reverence to Taddeo’s craftsmanship in smaller scale work, like many of his contemporaries in the trecento. Around 1401, Taddeo painted the celebrated altarpiece, "Assumption of the Virgin" and scenes from the "Passion", in Montepulciano. The intention of this piece was for religious and devotional functions. Taddeo worked to accommodate the established conventions of altarpiece painting, while simultaneously stylizing the pieces to fit their respective site. In 1403, Taddeo produced two works in Perugia, now on display in their public gallery. The "Virgin and Child with two Angels and St Bernard" and "Descent of the Holy Ghost". These two works showcase Taddeo’s superior talents, exhibiting delicate coloring and vast human expression; though they have been painted over throughout the years.