This book examines the figure of Duke Theudemir, one of the last great nobles of the Kingdom of Toledo, and the impact of his career on the transfer of power between the Visigothic nobility and the Arab conquerors. In the historical record, Theudemir appears as the archetypal ambitious aristocrat involved in the complex political intrigues that led to the ruin of the Visigothic Kingdom of Toledo in 711. Using this as a springboard, the book also analyzes the complex historical and administrative situation in the southeast of the Iberian Peninsula between the Byzantine invasion and the Arab occupation. Finally, the important archaeological site of Pla de Nadal (Ribarroja de Turia, Valencia) and its identification with the original power centre of Duke Theudemir is considered.