The Spanish era or era of Caesar (Latin: Æra Hispanica) was a dating system commonly used in the states of the Iberian Peninsula from the 3rd century until the 14th–15th centuries, when it was phased out in favour of the Anno Domini system. Year one of this calendar era coincides with what is now known as 38 BC, possibly 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 Iberia.
To convert an Anno Domini (AD) date to the corresponding year in the Spanish era, add 38 to the Anno Domini year, such that Era 941 would be equivalent to AD 903.
Official usage ceased in different parts of the peninsula at different times: Aragon in AD 1349, Valencia 1358, Castile 1383, and Portugal 1422. While the year officially began on 1 January under the Spanish era, that was changed to 25 December when the Anno Domini system was adopted (while the Church used 11 January).
- Roth, Norman. Medieval Iberia: An Encyclopedia. Routledge, 2003, p. 190