The history of Gilan is not very clear till the 6th century BC. or till the time that the Greek historians clarified some sections of Iranian history. But archaeological excavations show that the antiquity of the territory in the southern parts of the Caspian Sea dates back to the time prior to the last Ice Age, estimated around 50-150 millennium BC. Some historians believe that human civilization has emerged from the southern coasts of the Caspian Sea, extending westwards specially towards Mesopotamia.
Historical records of the Gilan civilization dates to several millennium BC. During this period, the 'Kasis' or the resident tribes of this region migrated to other areas for attaining better lands. Meanwhile, some groups of migrant tribes including Aryans migrated to this region due to climatic changes and the increase of frigidity in their territory. Due to the mingling of migrant tribes with the indigenous residents of the region, several new clans were formed, of which, the two tribes of 'Gill and 'Daylam' formed a majority. In the 6th century BC, the inhabitants of Gilan allied with Koorush (Cyrus) the Achaemenian and overthrew the Medes.
On the defeat of the Achaemenian Dynasty by Alexander the Macedonian, Iran came under their control. Thereafter, the Seleucidians took over the power. At that time, the local governors ruled independently. In the Sassanide era, Gilan lost its independence to some extent and Ardeshir Babakan overcame the local governors. During the Abbasid Caliphate, the Alavian (Shi'ites) who lived in the mountainous areas of Daylam, tried to severe the control of the Abbasid Caliphs from Iran. Consequently, the two united. Around the year 290 AH., the people of Gilan accepted the Shi'ite religion and tried to expand it. In this period some dynasties having Gilani and Daylami origins appeared on the historical scene in Iran.
One of the most dynasties as such was the 'Al Bouyeh', who even attacked Baqdad, the capital of the Abbasid Calipahte, and defeated the Abbasid Caliph. In the 7th century AH., the Mongols tried to conquer Gilan. But due to geographical conditions and lack of accessibility, they failed to get there till the early 8th century AH. Finally, Soltan Mohammad Khodabaneh or 'Oljaito' temporarily conquered this territory.
The Gilacks also payed an important role in the Constitutional Revolution in Iran. They conquered Tehran after two days of the attack of Mohammad Ali Shah in 1908 AD. Moreover, their contribution to the movement of ' Mirza Koochak Khan Jangali'or the 'Jungle Movement' and accounts as a glorious event in the history of this region.