are generally considered the most innovative (least conservative) among the Romance languages. Characteristic Gallo-Romance features generally developed earliest and appear in their most extreme manifestation in the Langue d'oïl, gradually spreading out along riverways and transalpine roads. In some ways, however, the Gallo-Romance languages are conservative. The older stages of many of the languages preserved a two-case system consisting of nominative and oblique, fully marked on nouns, adjectives and determiners, inherited almost directly from the Latin nominative and accusative and preserving a number of different declensional classes and irregular forms. The languages closest to the oïl epicenter preserve the case system the best, while languages at the periphery lose it early. Notable characteristics of the Gallo-Romance languages are: Early loss of unstressed final vowels other than — a defining characteristic of the group. Further reductions of final vowels in Langue d'oïl and many Gallo-Italic languages, with the feminine and prop vowel merging into , which is often subsequently dropped. Early, heavy reduction of unstressed vowels in the interior of a word (another defining characteristic). Loss of final vowels phonemicized the long vowels that used to be automatic concomitants of stressed open syllables. These phonemic long vowels are maintained directly in many Northern Italian dialects; elsewhere, phonemic length was lost, but in the meantime many of the long vowels diphthongized, resulting in a maintenance of the original distinction. The langue d'oïl branch is again at the forefront of innovation, with no less than five of the seven long vowels diphthongizing (only high vowels were spared). Front rounded vowels are present in all branches of Gallo-Romance. usually fronts to , and secondary mid front rounded vowels often develop from long or . Extreme lenition (i.e. multiple rounds of lenition) occurs in many languages especially in Langue d'oïl and many Gallo-Italian languages. The Langue d'oïl, Swiss Rhaeto-Romance languages and many of the northern dialects of Occitan have a secondary palatalization of and before , producing different results from the primary Romance palatalization: e.g. centum "hundred" > cent , cantum "song" > chant . Other than the Occitano-Romance languages, most Gallo-Romance languages are subject-obligatory (whereas all the rest of the Romance languages are pro-drop languages). This is a late development triggered by progressive phonetic erosion: Old French was still a null-subject language, and this only changed upon loss of secondarily final consonants in Middle French. Pidgins, creoles, and mixed languages Some Romance languages have