Caspian Sea

The sea approaches the mountain wall of the Caucasus at Derbent, leaving a narrow strip of coast that has long been guarded by fortifications. The city's walls once extended into the Caspian itself, controlling passage by water as well as land. Peter the Great captured Derbent during his Persian campaign in 1722, but Russia returned it to Persia under the treaty of Ganja in 1735.