Calahorra (anc. Calagurris), a city of northern Spain, in the province of Logroño; on the left bank of the river Cidacos, which enters the Ebro 3 m. E., and on the Bilbao-Saragossa railway. Pop. (1900) 9475. Calahorra is built on the slope of a hill overlooking the wide Ebro valley, which supplies its markets with an abundance of grain, wine, oil and flax. Its cathedral, which probably dates from the foundation of the see of Calahorra in the 5th century, was restored in 1485, and subsequently so much altered that little of the original Gothic structure survives. The Casa Santa, annually visited by many thousands of pilgrims on the 31st of August, is said to contain the bodies of the martyrs Emeterius and Celedonius, who were beheaded in the 3rd or 4th century, on the site now occupied by the cathedral. Their heads, according to local legend, were cast into the Ebro, and, after floating out to sea and rounding the Iberian peninsula, are now preserved at Santander.

The chief remains of the Roman Calagurris are the vestiges of an aqueduct and an amphitheatre. Calagurris became famous in 76 B.C., when it was successfully defended against Pompey by the adherents of Sertorius. Four years later it was captured by Pompey's legate, Afranius, after starvation had reduced the garrison to cannibalism. Under Augustus (31 B.C.-A.D. 14) Calagurris received the privileges of Roman citizenship, and at a later date it was given the additional name of Nassica to distinguish it from the neighbouring town of Calagurris Fibularensis, the exact site of which is uncertain. The rhetorician Quintilian was born at Calagurris Nassica about A.D. 35.