The Santerno is a river in

Romagna Romagna ( rgn, Rumâgna) is an Italian historical region that approximately corresponds to the south-eastern portion of present-day Emilia-Romagna, North Italy. Traditionally, it is limited by the Apennines to the south-west, the Adriatic to t ...

northern Italy Northern Italy ( it, Italia settentrionale, it, Nord Italia, label=none, it, Alta Italia, label=none or just it, Nord, label=none) is a geographical and cultural region in the northern part of Italy. It consists of eight administrative regions ...

. It is a major tributary of the river

Reno Reno ( ) is a city in the northwest section of the U.S. state of Nevada, along the Nevada-California border, about north from Lake Tahoe, known as "The Biggest Little City in the World". Known for its casino and tourism industry, Reno is the c ...

. In

Roman Roman or Romans most often refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a letter ...

times, it was known as the ''Vatrenus'' (small ''Renus''), although, in the

Tabula Peutingeriana ' (Latin Language, Latin for "The Peutinger Map"), also referred to as Peutinger's Tabula or Peutinger Table, is an illustrated ' (ancient Roman road map) showing the layout of the ''cursus publicus'', the road network of the Roman Empire. The m ...

, it was already identified as the ''Santernus''. It rises near the Futa Pass, at of elevation, in the Apennine ridges facing the plateau of

Firenzuola Firenzuola is a ''comune'' (municipality) in the Metropolitan City of Florence in the Italian region Tuscany, located about northeast of Florence. Firenzuola borders the following municipalities: Barberino di Mugello, Borgo San Lorenzo, Castel ...

in the

Metropolitan City of Florence The Metropolitan City of Florence ( it, Città Metropolitana di Firenze) is an administrative division called metropolitan city in the Tuscany region, Italy. Its capital is the city of Florence. It replaced the Province of Florence. It was first c ...

. Beyond Firenzuola, it flows northeast through the

province of Bologna The province of Bologna ( it, provincia di Bologna) was a province in the Emilia-Romagna region of Italy. Its provincial capital was the city of Bologna. The province of Bologna covered an area of and had a total population of 1,004,323 inhabitan ...

near

Castel del Rio Castel del Rio ( rgn, Castel d'e' Rì) is a ''comune'' (municipality) in the Metropolitan City of Bologna in the Italian region Emilia-Romagna, located about southwest of Bologna. Historically, the town's countryside is a large producer of ches ...

, where it is crossed by a famous medieval bridge, the ''Ponte degli

Alidosi The Alidosi or Alodosi are a family of Romagna, Italy, who held the ''signoria'' of the city of Imola during the Late Middle Ages. They were originary of the Santerno valley. History During the 13th century, the Alidosi supported the Guelph ca ...

''. It then flows past

Fontanelice Fontanelice ( rgn, Funtâna) is a ''comune'' (municipality) in the Province of Bologna in the Italian region Emilia-Romagna, located about southeast of Bologna. As of 31 December 2004, it had a population of 1,884 and an area of .All demographics ...

Borgo Tossignano Borgo Tossignano ( rgn, Borg Tusgnàn) is a ''comune'' (municipality) in the Province of Bologna in the Italian region Emilia-Romagna, located about southeast of Bologna. Borgo Tossignano borders the following municipalities: Casalfiumanese, Caso ...

Casalfiumanese Casalfiumanese ( rgn, Casêl Fiumanés) is a ''comune'' (municipality) in the Metropolitan City of Bologna in the Italian region Emilia-Romagna, located about southeast of Bologna. Casalfiumanese borders the following municipalities: Borgo Tossi ...

, and, once in the

Pianura Padana The Po Valley, Po Plain, Plain of the Po, or Padan Plain ( it, Pianura Padana , or ''Val Padana'') is a major geographical feature of Northern Italy. It extends approximately in an east-west direction, with an area of including its Venetic ex ...

(the

Po River The Po ( , ; la, Padus or ; Ligurian language (ancient), Ancient Ligurian: or ) is the longest river in Italy. It flows eastward across northern Italy starting from the Cottian Alps. The river's length is either or , if the Maira (river), Mair ...

's valley),

Imola Imola (; rgn, Jômla or ) is a city and ''comune'' in the Metropolitan City of Bologna, located on the river Santerno, in the Emilia-Romagna region of northern Italy. The city is traditionally considered the western entrance to the historical re ...

. The river forms the border between the province of Bologna and the

province of Ravenna The province of Ravenna ( it, provincia di Ravenna; ) is a province in the Emilia-Romagna region of Italy. Its capital is the city of Ravenna. As of 2015, it has a population of 391,997 inhabitants over an area of , giving it a population density ...

for a distance before entering the province of Ravenna. It then empties into the Reno near Argenta. It is probable that, in ancient times, the river flowed eastward from

Bagnacavallo Bagnacavallo ( rgn, Bagnacavàl) is a town and ''comune'' in the province of Ravenna, Emilia-Romagna, Italy. The Renaissance painter Bartolomeo Ramenghi bore the nickname of his native city. Main sights *''Castellaccio'' (15th century) * Gia ...

, as confirmed be the existence of a ''

frazione A ''frazione'' (plural: ) is a type of subdivision of a ''comune'' (municipality) in Italy, often a small village or hamlet outside the main town. Most ''frazioni'' were created during the Fascist era (1922–1943) as a way to consolidate territ ...

'' of

Ravenna Ravenna ( , , also ; rgn, Ravèna) is the capital city of the Province of Ravenna, in the Emilia-Romagna region of Northern Italy. It was the capital city of the Western Roman Empire from 408 until its collapse in 476. It then served as the cap ...

called Santerno. In those days, after Imola, the river divided into two branches, one moving northeast toward Ravenna, the other continuing northward to join the Po. The Ravenna branch disappeared, most likely in the eighth century. Once the late course of the river was modified, and protective measures were taken in the 1880s, the Santerno was famous for its serious floods. Fourteen were recorded between 1679 and 1778.

Footnotes

Rivers of the Province of Florence Rivers of the Province of Bologna Rivers of the Province of Ravenna Rivers of the Apennines Rivers of Italy {{Italy-river-stub