evidence: The Sea of Azov, scene of a new escalation in tensions between Ukraine and Russia, is joined to the Black Sea by a narrow strait that is a vital shipping lane for both the rival nations. [...] Wedged between Russia, Ukraine and Crimea, the Sea of Azov is a northern extension of the Black Sea to which it is linked via the Strait of Kerch, which is just 15 kilometres (nine miles) wide. [...] The Sea of Azov is the shallowest sea in the world, with a maximum depth of just 14 metres (46 feet). It is also small at around 360 kilometres long and 180 kilometres wide.