It is probable that the "invasion" was not from outside the kingdom; because the word regnum can refer to the office of the king, it is likely that Roderic merely usurped the throne. Nonetheless, it is possible that Roderic was a regional commander (dux of Baetica in later, legendary sources) or even an exile when he staged his coup.
The "tumult" which surrounded this usurpation was probably violent, though whether or not it involved the deposition or assassination of the legitimate king, Wittiza, or was a consequence of his recent natural death has divided scholars. Some scholars believe that the king Achila, who ruled in opposition to Roderic, was in fact Wittiza's son and successor and that Roderic had tried to usurp the throne from him.
The senate with which Roderic accomplished his coup was probably composed of the "leading aristocrats and perhaps also some of the bishops." The participation of churchmen in the revolt is disputed, some arguing that the support of the bishops would not have led to the act being labelled a usurpation. The body of leading temporal and ecclesiastical lords had been the dominant body in determining the Visigothic succession since the reign of Reccared I. The palatine officials, however, had not been much affected by royal measures to decrease their influence in the final decades of the kingdom, as their effecting of a coup in 711 indicates.
A Visigothic regnal list mentions "Ruderigus" as having reigned seven years and six months, while two other continuations of the Chronicon Regum Visigothorum record Achila's reign of three years. In contrast to the regnal lists, which cannot be dated, the Chronicle of 754, written at Toledo, says that "Rudericus" reigned for a year. Roderic's reign is usually dated to begin in 710 (rarely as early as 709) or, more commonly, 711 and to have extended until late in 711 or 712. Achila's reign probably began shortly after Roderic's and lasted until 713.
Roderic made several expeditions against the invaders before he was deserted by his troops and killed in battle in 712. The chronicler of 754 claims that some of the nobles who had accompanied Roderic on his last expedition did so out of "ambition for the kingdom", perhaps intending to allow him to die in battle so that they could secure the throne for one of themselves. Whatever their intentions, most of them seem to have died in the battle as well. Other historians have suggested that low morale amongst the soldiery because of Roderic's disputed succession was the cause of defeat. The majority of Roderic's soldiers may have been poorly trained and unwilling slave conscripts; there were probably few freemen left fighting for the Goths.
The location of the battle is debatable. It probably occurred near the mouth of the Guadalete river, hence its name, the Battle of Guadalete. According to Paul the Deacon, the site was the otherwise unidentifiable "Transductine promontories".
According to the Chronicle of 754, the Arabs took Toledo in 711 and executed many nobles still in the city on the pretense that they had assisted in the flight of Oppa, a son of Egica. Since this took place, according to the same chronicle, after Roderic's defeat, either the defeat must be moved back to 711 or the conquest of Toledo pushed back to 712; the latter is preferred by Collins. It is possible that the Oppa who fled Toledo and was a son of a previous king was the cause of the "internal fury" which wracked Hispania at the time recorded in the Chronicle. Perhaps Oppa had been declared king at Toledo by Roderic and Achila's rivals, either before Roderic's final defeat or between his death and the Arab capture of Toledo. If so, the death of the nobles who had "ambition for the kingdom" may have been Oppa's supporters who were killed in Toledo by the Arabs shortly after the battle in the south.
Roderic left a widow, Egilo, who later married one of the Arabic governors of Hispania.
The family of Wittiza then fled to Ceuta on the northern shore of the Maghreb. In Ceuta, Visigothic rivals of Roderic gathered along with Arians and Jews fleeing forced conversions at the hands of the Catholic bishops who controlled the Visigothic monarchy. The surrounding area of the Maghreb had recently been conquered by Musa Ibn Nosseyr, who established his governor, Tariq ibn Ziyad, at Tangier with a Moorish army of 1,700 men.
Julian, count of Ceuta, who the Arabs called Ilyan, was Roderic's vassal but also on increasingly good terms with Tariq, and the family of Wittiza. The Egyptian historian of the Muslim conquest, Ibn Abd-el-Hakem, related a century and a half later that Julian had sent one of his daughters to the Visigothic court at Toledo for education (and as a gauge for Julian's loyalty, no doubt) and that Roderic had made her pregnant. Later ballads and chronicles inflated this tale — she was known in Spanish as la Cava Rumía and attributed Julian's enmity to Roderic's poor treatment of his daughter.
Some historians argue that personal power politics may have played a larger part as both Julian and Wittiza's family sought power in the Visgothic kingdom. In exchange for lands in Al-Andalus (the Arab name for the area which the Visigoths still called by its Roman name Hispania) Julian's ships carried Tariq's troops across the Straight of Hercules (Strait of Gibraltar).
In the spring of 711, Roderic was campaigning against the Basques and Franks near the north Iberian town of Pamplona. Tariq, briefed by Julian, whom he left behind among the merchants, crossed into Visigothic Hispania with a reconnaissance force of some 1,700 men, sailing by night and keeping their size inconspicuous. Ibn Abd-el-Hakem reported that "the people of Andalus did not observe them, thinking that the vessels crossing and recrossing were similar to the trading vessels which for their benefit plied backwards and forwards." Tariq and his men marched up as far as Cartagena on the coast, then to Cordoba, where resistance from the local Visigothic garrison was eventually driven back to the city.
Roderic marched his forces south and met Tariq's men at the Battle of the Rio Barbate or the Battle of Guadalete in the Province of Cadiz. The battle occurred on July 19, 711. Roderic's army of around 25,000 men was defeated by Tariq's force of approximately 7,000.
Roderic is believed to have died in the battle, though his exact fate is unknown. The Visigothic army was defeated when the wings commanded by Roderic's relatives Sisbert and Osbert deserted. His defeat left the Visigoths disorganized and leaderless, and the survivors fled north to Écija near Seville.
The great majority of Roderic's court was also believed killed in the battle (an old tradition says he survived and tried to reach the northern peninsula, in order to defeat the invaders, but died when he was at Guarda, in modern Portugal, where some claim his body was buried). The resulting power vacuum is believed to have assisted Tariq's lord, Musa ibn Nusair, in conquering most of the Iberian Peninsula by 718 and the whole of the Visigothic territories by 725.
The Scottish writer Walter Scott, and the English writers Walter Savage Landor, and Robert Southey had handled the legends associated with these events poetically: Scott in "The Vision of Don Roderick" in 1811, Landor in his tragedy Count Julian in 1812, and Southey in Roderick, the Last of the Goths in 1814.
The American writer Washington Irving retells the legends in his 1835 Legends of the Conquest of Spain, mostly written while living in that country. These consist of "Legend of Don Roderick", "Legend of the Subjugation of Spain", and "Legend of Count Julian and His Family."
Rodrigo by George Frideric Handel is an operatic version of the conflict between Roderic and Julian.
The common Spanish first name Rodrigo, the common family name derived from it Rodríguez (meaning Son of Rodrigo) and the Portuguese equivalent Rodrigues might all be directly or indirectly derived from the Visigothic king's name.