In the middle of the first millennium A.D. a fort was built in Iru at the foot of which formed an open settlement. The fort was destroyed by fire in the 9th century, however, it was soon rebuilt and reinforced by a limestone wall.

Apparently Iru was the most significant trading centre of the area and its importance was further enhanced by the navigable river enabling the foreign traders’ participation in the local economy. Presumably in the first half of the 11th century the fort and settlement in Iru were abandoned for good, most probably due to the fact that the Earth’s surface rise had formed rapids in the river thus making it too shallow for the new larger ships replacing the earlier smaller ones. The trading centre was moved westward from the mouth of the river, near the cliff bank of Toompea by the shores of the Bay of Tallinn.