It possesses the five vowels a, i, u, e, o, both short and long, and one pure diphthong, au.
It was not by any means exclusively the " battle of a diphthong."
Thus the long i in ride, wine, &c., has become the diphthong ai, and the name of the symbol I is itself so pronounced.
Latin e was identified with a native diphthong ei, and becomes zvy, as in rhwyf from remus.
Latin au becomes o (cOla, c a u s a; or, a U r u m); Old Catalan has kept the diphthong better, but possibly we- should attribute the examples of au which are met with in texts of the 13th and 14th centuries to the literary influence of Provence.