The Caucasus, at the boundary between Europe and Asia, has been known since the early Middle Ages for its linguistic diversity; Arab geographers called this area the "mountain of tongues." UCSB faculty and graduate student researchers concentrate on West and East Caucasian languages, contributing to their linguistic documentation while pursuing a theoretical and analytical focus on aspects of phonology, grammar, and typology. Research to date has identified a number of typologically unusual features in the Caucasus, including rich consonant inventories (especially ejectives and pharyngealization), elaborate gender and case systems, and complex verb morphology interacting with clause structure and systems of clause combining. In addition to representatives of language families represented elsewhere in Eurasia (in particular, Indo-European and Turkic), the Caucasus encompasses three language families whose relations to one another and to languages outside the Caucasus remain unclear: West Caucasian (including Abkhaz and Kabardian), East Caucasian (including Chechen, Avar, and Lezgian), and Kartvelian (including Georgian).