It shows Guidoriccio da Fogliano, the commander of the Sienese troops, on horseback against the background of a landscape in which the siege of Montemassi takes place.. For a long time it was assumed that the work was painted in 1330 by Simone Martini.

In the middle of the fresco Guidoriccio da Fogliano, a condottiero (mercenary officer) and commander of the Sienese troops, is depicted on horseback.

By decorating the meeting room of the Council of Nine with these images, it was made clear that these cities and castles were now the inalienable property of Siena.

Documents show that Simone Martini painted at least four of them: Montemassi and Sasso Forte in 1330, and Arcidosso and Castel Del Piano in 1331.

The Guidoriccio has been considered one of the first secular, i.e. strictly non-religious, portraits, and one of the first monumental landscape paintings in Western art.

Moran and Mallory suggested that the rider image was added to the fresco in 1351, after the death of Guidoriccio da Fogliano who had by then been reinstated as commander of the Sienese troops.

Moran and Mallory have stated that they were systematically thwarted by prominent Italian art historians and by the Sienese authorities.

[2] The debate took on a new dimension a few years later when a previously unknown fresco was discovered on the western wall of the Sala del Mappamondo.

The main issue in the Guidoriccio debate therefore no longer was whether perhaps the equestrian image had not been painted by Simone Martini, but whether the entire fresco could be attributed to him.

It has been suggested that the Guidoriccio was painted by Lippo Memmi, a brother-in-law of Simone Martini who had a similar style.

[2][3] The debate on the correct attribution of the Guidoriccio raged for decades in scientific journals as well as in the wider media; still no final conclusion has been reached.

The fact that Vasari in his famous painters' biography Le Vite from 1550 makes no mention of a work as prominent as the horseman fresco is seen by some as a reason to date it even later.