The city and kingdom were supposedly founded by a group of Aja migrants from Tado, a settlement along the Mono River, in the 12th or 13th century.

According to the Fon oral tradition, the Aja settlers that established themselves in the area of present-day Allada arrived in southern Benin around the 12th or 13th century coming from Tado, on the Mono River.

They established themselves in the area that currently corresponds to southern Benin, until c. 1600, when three brothers — Kokpon, Do-Aklin, and Te-Agdanlin — split the rule of the region amongst themselves: Kokpon took the capital city of Great Ardra, reigning over the Allada Kingdom, while his brother Do-Aklin founded Abomey (which would become capital of the Kingdom of Dahomey) and their brother Te-Agdanlin founded Little Ardra, also known as Ajatche, later called Porto Novo (literally, "New Port") by Portuguese traders (which is the current capital city of Benin).

In 1904, the kingdom was annexed by France, however it was allowed to continue to exist as a non-sovereign monarchy with its leaders being referred to as "chef supérieur".

The title of "king" was re-established in 1992 upon the coronation of Kpodégbé Togi Djigla, and the non-sovereign monarchy continues to this day.

[13] Primary sources from the 1690s state that Ardra's army moved in companies only during parades as they fought in loose formations on the battlefield.

[15] Slaves used to be captured from enemy states and passed on to European slavers bound for the Americas, the route which by repute the father of Toussaint L'Ouverture, the famous general that lead the slave rebellion of the Haitian revolution that lead Jean-Jacques Dessalines to establish the Empire of Haiti, had taken.

To quote from their sources, "Gaou Guinou, Minister of War and younger brother of the King of Allada, rather than succeeding to his father and ascending naturally to the throne, chose then to accompany his vanquished soldiers in exile.