Even on the supposition that a St. Firmin, native of Pampeluna, was martyred during the persecution of Diocletian, it is certain that the first bishop known to history is St. Eulogius, who defended the divinity of Christ in the councils held during the middle of the 4th century.
The succession of bishops continued under the Arab domination: after St. Eulogius, in 851, we find there Sisemund, a man of great sagacity.
The earliest account of the Quran in a language other than Arabic is credited to Eulogius, who translated Sura al-Ahzab verse 37, around the year 857.