Derbent, also historically known as Darband, or Derbend, is the southernmost city in Russia. It is situated along the southeastern coast of the Republic of Dagestan, occupying the narrow gateway between the Caspian Sea and the Caucasus Mountains, and connecting the Eurasian Steppe to the north and the Iranian Plateau to the south. Derbent covers an area of 69.63 square kilometres (26.88 sq mi) with a population of roughly 120,000 residents.

Derbent is considered the oldest city in Russia, with historical documentation dating to the 8th century BC, making it one of the oldest continuously inhabited cities in the world. Due to its strategic location, over the course of history, the city changed ownership many times, particularly among the Persian, Arab, Mongol, Timurid, and Shirvan kingdoms. In the early 19th century, the city came under control of the Russian Empire through the Treaty of Gulistan signed with Qajar Iran.

Derbent is derived from Persian "Darband" (Persian: دربند, lit. 'Door/opening in a Barrier', from dar "door/gate" + band "barrier/dam", lit., "gate in the barrier"), referring to the eastern-most pass in the high Caucasus Mountains (whence the putative "barrier/dam") on the beaches of the Caspian Sea. (The other pass, the Darial Pass, is in the Central Caucasus Mountains, and likewise carries a Persian name, standing for "the Alan Pass/gate" – with the Alans being the modern Iranic Ossetians.)

It is often identified with the Gates of Alexander, a legendary barrier supposedly built by Alexander the Great in the Caucasus. The Persian name for the city came into use at the end of the 5th or the beginning of the 6th century AD, when the city was re-established by Kavadh I of the Sassanid dynasty of Persia, but Derbent was probably already in the Sasanian sphere of influence as a result of the victory over the Parthians and the conquest of Caucasian Albania by Shapur I, the second shah of the Sassanid Persians. The geographical treatise Šahrestānīhā ī Ērānšahr written in Middle Persian mentions the old name of the fortress – Wērōy-pahr (The Georgian Guard):

šahrestan [ī] kūmīs [ī] panj-burg až-i dahāg pad šabestān kard. māniš [ī] *pārsīgān ānōh būd. padxwadayīh [ī] yazdgird ī šabuhrān kard andar tāzišn ī čōl wērōy-pahr [ī] an ālag. (The city of Kūmīs of five towers Aži Dahag made it his own harem. The abode of the Parthians was there. In the reign of Yazdgird, the son of Šabuhr made it during the invasion of the Čōl, at the boundary of the Georgian Guard.).

-Wėrōy-pahr: "The Georgian Guard" The old name of the fortress at Darband;...

In Arabic texts the city was known as "Bāb al-Abwāb" (Arabic: بَاب ٱلْأَبْوَاب, lit. 'Gate of all Gates'), simply as "al-Bāb" (Arabic: ٱلْبَاب, lit. 'The Gate') or as "Bāb al-Hadid" (Arabic: بَاب ٱلْحَدِيد, lit. 'Gate of Iron'). A similar name meaning "Iron Gate" was used by Turkic peoples, in the form "Demirkapi".

Derbent's location on a narrow, three-kilometer strip of land in the North Caucasus between the Caspian Sea and the Caucasus Mountains is strategic in the entire Caucasus region. Historically, this position allowed the rulers of Derbent to control land traffic between the Eurasian Steppe and the Middle East. The only other practicable crossing of the Caucasus ridge was over the Darial Gorge.