The northern part of the province is part of territory of South (Iranian) Talysh. At the center of the province is the main city of Rasht. Other towns in the province include Astara, Astaneh-e Ashrafiyyeh, Fuman, Lahijan, Langrud, Masouleh, Manjil, Rudbar, Roudsar, Shaft, Talesh, and Soumahe Sara.
The main harbor port is Bandar-e Anzali (previously Bandar-e Pahlavi).
It seems that the Gelae (Gilites) entered the region south of the Caspian coast and west of the Amardos River (later Safidrud) in the second or first century B.C.E. Pliny identifies them with the Cadusii who were living there previously. It is more likely that they were a separate people, had come from the region of Dagestan, and taken the place of the Kadusii. The fact that the native inhabitants of Gilan have originating roots in the Caucasus is supported by genetics and language, as Gilaks are genetically closer to ethnic peoples of the Caucasus (such as the Georgians) than they are towards other ethnic groups in Iran. Their languages shares certain typologic features with Caucasian languages.
It was the place of origin of the Buyid dynasty. The people of the province had a prominent position during the Sassanid dynasty, so that their political power extended to Mesopotamia.
The first recorded encounter between Gilanis and Deylamite warlords and invading Muslim Arab armies was at the Battle of Jalula in 637 AD. Deylamite commander Muta led an army of Gils, Deylamites, Persians and people of the Rey region. Muta was killed in the battle, and his defeated army managed to retreat in an orderly manner.
However, this appears to have been a Pyrrhic victory for the Arabs, since they did not pursue their opponents. Unlike the Russians, Muslim Arabs never managed to conquer Gilan as they did with other provinces in Iran. Gilanis and Deylamites successfully repulsed all Arab attempts to occupy their land or to convert them to Islam. In fact, it was the Deylamites under the Buyid king Mu'izz al-Dawla who finally shifted the balance of power by conquering Baghdad in 945. Mu'izz al-Dawla, however, allowed the Abbasid caliphs to remain in comfortable, secluded captivity in their palaces.
In the 9th and 10th centuries AD, Deylamites and later Gilanis gradually converted to Zaidite Shi'ism. Several Deylamite commanders and soldiers of fortune who were active in the military theaters of Iran and Mesopotamia were openly Zoroastrian (for example, Asfar Shiruyeh a warlord in central Iran, and Makan, son of Kaki, the warlord of Rey) or were suspected of harboring pro-Zoroastrian (for example Mardavij) sentiments. Muslim chronicles of Varangian (Rus, pre-Russian Norsemen) invasions of the littoral Caspian region in the 9th century record Deylamites as non-Muslim. These chronicles also show that the Deylamites were the only warriors in the Caspian region who could fight the fearsome Varangian vikings as equals. Deylamite infantrymen had a role very similar to the Swiss Reislufer of the Late Middle Ages in Europe. Deylamite mercenaries served as far away as Egypt, Islamic Spain, and in the Khazar Kingdom.
Buyids established the most successful of the Deylamite dynasties of Iran.
In the 9th-11th century AD, there were repetitively military raids undertaken by the Rus' between 864 and 1041 on the Caspian Sea shores of Iran, Azerbaijan, and Dagestan as part of the Caspian expeditions of the Rus'. Initially, the Rus' appeared in Serkland in the 9th century traveling as merchants along the Volga trade route, selling furs, honey, and slaves. The first small-scale raids took place in the late 9th and early 10th century. The Rus' undertook the first large-scale expedition in 913; having arrived on 500 ships, they pillaged the westernmost parts of Gorgan as well as Gilan and Mazandaran, taking slaves and goods.
The Turkish invasions of the 10th and 11th centuries CE, which saw the rise of Ghaznavid and Seljuq dynasties, put an end to Deylamite states in Iran. From the 11th century CE to the rise of Safavids, Gilan was ruled by local rulers who paid tribute to the dominant power south of the Alborz range but ruled independently.
In 1307 the Ilkhan ljeit conquered the region after witnessing a Pyrrhic victory. This was the first time the region came under the rule of the Mongols after the Ilkhanid Mongols and their Georgian allies failed to do it in the late 1270s. After 1336, the region seems to be independent again.
Before the introduction of silk production (date unknown, but definitely a pillar of the economy by the 15th century AD), Gilan was a poor province. There were no permanent trade routes linking Gilan to Persia. There was a small trade in smoked fish and wood products. It seems that the city of Qazvin was initially a fortress-town against marauding bands of Deylamites, another sign that the economy of the province did not produce enough on its own to support its population. This changed with the introduction of the silk worm in the late Middle Ages.