Archaeological investigations at the hill fort of Keava have revealed the remains of five fortification phases dating from the 5th–6th centuries to the early 13th century. The earliest two phases (forts I and II) were recognizable only in the area of the ramparts as definite fortification structures. The later phases (forts III–V) since the late 10th – early 11th century were observable both in the area of the ramparts (defensive structures) and in the compound (building remains), as well as in the find assemblage. The hidden gateway beneath the rampart was first built during phase III; in later times, however, it was repeatedly rebuilt. Stone material was widely used in the construction of the rampart and the gateway of the last fort, which dated from the late 12th – early 13th century. The fort was finally captured by the crusaders, most likely in 1224; they dug a large hollow on the northern hill slope and dropped the rampart.