The history of Baku dates back to 1st millennium BCE, with the earliest written evidence from 6th century CE, however. The city was the location of an important fire temple of the Persian religion of Zoroastrianism, which was prevalent before the Islamic conquest of Iran.
The first written reference to Baku dates from 885, although archaeologists have found remains of a settlement predating by several centuries the birth of Jesus. The city became important after an earthquake destroyed Shemakha and in the 12th century, leading Shirvanshah Ahistan I to made Baku the new capital. In 1813, Russia signed the Treaty of Gulistan with Persia, which provided for the cession of Baku and most of the Caucasus from Iran and their annexation by Russia.
The center of Baku is the old town, which is also a fortress. In December 2000, the "Walled City of Baku with the Shirvanshah's Palace and Maiden Tower" (called the "inner town") became the first location in Azerbaijan classified as a World Heritage Site by UNESCO. Most of the walls and towers, strengthened after the Russian conquest in 1806, survive. This section is picturesque, with its maze of narrow alleys and ancient buildings. Wander the cobbled streets past the Palace of the Shirvanshahs, two caravansaraies (ancient inns), the 11th century Maiden Tower (nice view of the harbor), the baths and the Djuma Mosque (it used to house the Carpet and Applied Arts Museum, but now is a mosque again; the carpets got moved to the former Lenin museum). The old town also has dozens of small mosques, often without any particular sign to distinguish them from the next building.