The Spanish era, Hispanic era or Caesar era refers to the dating system used in Hispania until the 14th century, when the Anno Domini system was adopted. It began with year one in what is 38 BC, probably the date of a new tax imposed by the Roman Republic on the subdued population of Iberia. Whatever the case, the date signifies the beginning of the Pax Romana in Hispania. To convert from a date in the Christian era to the corresponding year in the Hispanic era, add 38 to the Christian era year. A date in the Hispanic era was written thus: "Era CMXLI" for "anno domini [AD] 903".
The use of the Hispanic era probably began in Iberia in the 3rd century. The reason for its particular popularity is unknown. Usage died out in different parts of the Iberian peninsula at different times: