The original form of the mitre was that of the early papal tiara (regnum), i.e.
If there was thus only a customary and unwritten law (and William of Tyre definitely speaks of a jus consuetudinarium under Baldwin III., quo regnum regebatur), then the "Letters of the Sepulchre" are a myth - or rather, if they ever existed, they existed not as a code of written law, but, perhaps, as a register of fiefs, like the Sicilian Defetarii.
He travelled in Germany, France and Italy, in quest of the most eminent teachers and the best books dealing with the human frame, and published, as the results of his inquiries among other works, his Oeconomia regni animalis (London, 1740-1741) and Regnum animale (the Hague, 1744-1745; London, 1745).
We have little doubt that Abyssinia was the "regnum" here indicated, though it was a mistake to identify the Abyssinian Church with the Nestorians.
The natural advantages of its site and its position with relation to the pass over the Alpis Cottia (Mont Genevre; see CoTTri Regnum) made it important in early times, though it cannot have been very strongly fortified, inasmuch as Hannibal, after crossing the Alps in 218 B.e., was able to take it after a three days' siege.