The Caucasus, a popular saying goes, is a ‘mountain of tongues’. Describing this region requires a strong constitution, determination and brilliance because, as Christoph Baumer writes in this magnificent book, ‘in many ways, the Caucasus region is a puzzle’.

That is something of an understatement. For one thing, the mountains usually referred to as the Caucasus are in fact part of two geologically distinct ranges: the Greater Caucasus that is around 100 kilometres wide and ten times the length, spans the land between the Black and Caspian Seas and acts as a climatic valve, blocking off like a plug cold...