Fresco of Pope Innocent III in the Monastery of Sacro Speco in Subiaco ca. 1300
Richard H. Helmholz, “Magna carta and the ius commune,” The University of Chicago Law Review 66 (1999) 297-371
Magna carta and Canon Law:
Chapter 9: Suretyship (Fideiussor)
Pennington, “The Ius commune, Suretyship, and Magna carta,” Rivista internazionale di diritto comune 11 (2000) 255-274
Peter Landau, “Bürgschaft und Darlehen im Dekretalenrecht des 12. Jahrhunderts,” Festschrift für Dieter Medicus (Berlin: 1999) 297-316
De rege Johanne, British Library, Cotton Claudia D.ii. folio, fol. 116r