Bernardo del Carpio goes unmentioned by any chronicler until 1236. However, the early chronicles do have some things to say about Alfonso the Chaste, his Great namesake, and Charlemagne and Roncesvalles. An incomplete summary of the historiography follows.
The real Alfonso II was born in 760, became king in 791, (probably) never married, and died in 842. Alfonso III was born 848, became king of Galicia, Leon, and Asturias in 866, married Princess Jimena of Pamplona, and died in 910.
Einhard: Einhard’s Life of Charles the Great was written sometime in the early 800s, after Charles’ death.
King Alfonso of Asturias and Galicia always called himself Charles’ man [vassal] in his letters.
Chronica Albeldense: Also called the Epitome Ovediense, written 881.
Alfonso the Chaste, also called the Great, founded Oviedo. He reigned for fifty-one years, though in his eleventh year he was deposed and locked in the monastery of Abelania. After escaping, he built many churches, adopted the Toledan [Mozarabic] Rite, and gave refuge in Asturias to a certain Muhammad who was fleeing the King of Cordova. Muhammad betrayed him, however, and Alfonso killed him in battle. He never married.
Alfonso son of Ordoño (the Great) conquered at Ebrellos. He took the throne at eighteen, fought civil and foreign wars, and built many churches. In 916, Almundar, son of King Mohamat, led an army from Cordova to Astorga and Leon. Part of his army was attacked at Polvorosa on the Órbigo by King Alfonso III, who killed almost 13,000 Moors. When the news reached Almundar, he retreated. Alfonso fought more wars and built many churches.
Roncesvalles and Charlemagne are nowhere mentioned.
Chronicle of Alfonso III: From the early 900s, written at the behest of Alfonso III. It exists in two major reactions, known as the Crónica Rotensis and the later and longer Crónica ad Sebastianum. There are also two minor redactions, simply called the Third and the Fourth. All versions printed 1918 by Zacarías García Villada.
Fourth Redaction only: In Era 815 [AD 777] Ibn al-Arabi, who held Saragossa under Abd-er-Rahman, rebelled and asked King Charles of the Franks for aid, who had been fighting the Saxons for thirty years. Charles was welcomed at Pamplona, and came to Saragossa, but did not take it, corrupted by gold. He destroyed “a certain city” on his way back, whose inhabitants ambushed him in Ruscidis Vallibus, where Egiardus, Anselmus, and Rotolanus died. The next year Charles became Emperor, AD 778. He reigned 47 years. (Copied, but not exactly, from Silense)
Chronicle of Alfonso III, MS Emilianse 39: [The Nota Emilianese, c. 1070] In Era 816 [AD 778] King Charles came to Saragossa. He had twelve nephews, each with three thousand knights in armor: Rodlane, Bertlane, Oggero Spatacurta [Shortsword] Ghigelmo Alcorbanitas [Hooknose], Olibero, and the bishop Don Toripini. Each spent a month in the king’s service. Charles’ vassals advised him to return home, which he did, leaving Roldan in the rearguard, where, in the Puerto de Sicera, in Rozaballes, the Saracens killed him.
Sampiro (1098) A continuation of the Chronicle of Alfonso III, covering 866 to 982. Incorporated into the Historia Silense.
The Historia Silense (c. 1100-1130) does not mention Bernardo. However, this chronicle is only interested in the deeds of kings, and ignores the Counts of Castile entirely. It can be most conveniently found in the appendices to volume XVII of España Sagrada.
After fighting the Saxons for 33 years, Charles entered Spain between the reigns of Roderick (d. 712) and Pelagius (r. 718-737), invited by a Moor named Hibinnaxalabi, king of Saragossa. He laid siege to Saragossa, but the Franks were corrupted by bribes and abandoned the war. They razed the walls of Pampelona, and their rearguard was attacked by the Navarrese, and Anselm, Egginhard, and Roland died.
The Chronicon of Bishop Pelagius of Oviedo (finished 1132), is the earliest (known) source to claim that Alfonso II the Chaste had a wife. According to Pelagius, her name was Bertinalda and she was related to the Royal House of France. Hence it has been suggested that Pelagius knew some version of the legend of Bernardo del Carpio, though makes no other allusions to that hero.
The Crónica Najerense, written by a Castilian around 1160 and championing Castilian independence, does not mention Bernardo del Carpio. However, it also ignores the Seven Sons of Lara and the Cid Campeador, whose stories are known to have been circulating at this date.
Roncesvalles was in the third year of King Silo , and is described in an account copied from the Silense. Charles was made Emperor the year after, and reigned for 47 years.
The Anales Toledanos Primeros (1219) (España Sagrada XXIII) assert that Alfonso the Chaste died in 850, Charlemagne entered Spain in 862 [most likely referring to Mainet, not to the beginning of the Spanish War], Roncesvalles “where the Twelve Peers died” was fought in 882, and Charlemagne died in 911.