Ingo Schwab's handsome edition of the material bearing on Alfonso x of Castile's campaign to establish a claim through his Hohenstaufen mother to succeed Frederick ii as Holy Roman Emperor has been almost twice as long in the making as the campaign itself took to implode. Launched in 1255, by 1273 when the pope delivered his coup de grâce, dispersing the string of Ghibelline sympathisers in Provence and North Italy, the alternative ‘much greater and better empire’, which the ruler of Granada had meanwhile been dangling before Alfonso, had disappeared from view and the learned but not terribly sensible king was well on his way to losing Castile itself to his son and heir. Good as it is to have the documentation of the matter reproduced in best MGH style, there is little here to provide students of the period with cause for surprise. Indeed it is remarkable how rarely the editor is able to improve upon at least his German predecessors’ work: witness, for example, his text of Alfonso's agreement with the commune of Marseilles in 1256 when placed alongside Scheffer-Boichorst's account of the matter published in 1888. And up to a point much the same goes for the work of Spanish scholars from Mondéjar to Ballesteros and beyond. Particularly welcome will be the fine plates of material in non-Spanish collections and the exemplary Namenregister of more than a hundred pages. Sad to say, what is lacking in this volume on the Castilian monarch is anything specifically Castilian, the inevitable consequence, it might be thought, of the fourteenth-century loss of the Castilian royal archive. But this neglects the possibility of relevant material awaiting discovery in Iberia's Kew (as it might have been). Where once protected by termagants trained to turn researchers approaching the place to stone, the archive of Toledo cathedral is now administered by custodians who are models of their kind. On another level, the authors’ introductory essay, which cites too little published in the last ten years, might have found room for M. González Jiménez and M. A. Carmona Ruiz's Documentación e itinerario de Alfonso X el Sabio (2012), for (dare one suggest as much?) The Mozarabic cardinal (2004; F. J. Hernández and this reviewer's study of Alfonso's chargé d'affaires impériales for much of this time) and, above all, for reference to the fundamental doctoral thesis of Maria Klein on his chancery functionaries during these years, La cancillería real castellana durante el reinado de Alfonso X: una aproximación prosopográfica (Seville 2014).