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In 552, "Khazars" invaded North-Eastern Caucasus and occupied northern lowlands of Dagestan. Reigning Shah of Persia Khosrau I (531—579), to protect his possessions from the new wave of nomads, began the construction of defensive fortifications in Derbent, that closed a narrow passage between the Caspian Sea and Caucasian mountains. Khosrau I owned fortress Gumik. The modern name "Derbent" is a Persian word (دربند Darband) meaning "gateway", which came into use in this same era, in the end of the 5th or the beginning of the 6th century CE, when the city was re-established by Kavadh I of the Sassanid dynasty of Persia.