The tornesel, tornesol, or tornese was a silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 coin of Europe in the late Middle Ages

Middle Ages

The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

 and the early modern era. It took its name from the denier Tournois, the denier

French denier

The denier was a Frankish coin created by Charlemagne in the Early Middle Ages. It was introduced together with an accounting system in which twelve deniers equaled one sou and twenty sous equalled one livre...

 of Tours

Tours

Tours is a city in central France, the capital of the Indre-et-Loire department.It is located on the lower reaches of the river Loire, between Orléans and the Atlantic coast. Touraine, the region around Tours, is known for its wines, the alleged perfection of its local spoken French, and for the...

.
Marco Polo

Marco Polo

Marco Polo was a Venetian merchant traveler from the Venetian Republic whose travels are recorded in Il Milione, a book which did much to introduce Europeans to Central Asia and China. He learned about trading whilst his father and uncle, Niccolò and Maffeo, travelled through Asia and apparently...

 referred to the tornesel in recounts of his travels to East Asia when describing the currencies of the Yuan Empire

Yuan Dynasty

The Yuan Dynasty , or Great Yuan Empire was a ruling dynasty founded by the Mongol leader Kublai Khan, who ruled most of present-day China, all of modern Mongolia and its surrounding areas, lasting officially from 1271 to 1368. It is considered both as a division of the Mongol Empire and as an...

. His descriptions were based on the conversion of 1 bezant

Bezant

Bezant is a medieval term for a gold coin from the Byzantine Empire, which term is derived from the Greek name Βυζάντιον for the relatively minor city which in the 4th c. became the capital of the Eastern Roman Empire, renamed Constantinople by the Roman Emperor Constantine the Great...

 = 20 groats = 133⅓ tornesel.
The tornese was a subunit of the Neapolitan

Neapolitan piastra

The piastra was the most common silver coin of the mainland Kingdom of Sicily, also known as the Kingdom of Naples. In order to distinguish it from the piastra issued on the island of Sicily, it is referred to as the "Neapolitan piastra" as opposed to the "Sicilian piastra". These two piastra were...

, Sicilian

Sicilian piastra

The piastra was the distinct currency of the Kingdom of Sicily until 1815. In order to distinguish it from the piastra issued on the mainland Kingdom of Sicily , it is referred to as the "Sicilian piastra" as opposed to the "Neapolitan piastra". These two piastra were equal but were subdivided...

, and Two Sicilies ducats.