Hakoinen sits in the older Nordic tradition of the hill fort: an easily defensible high point used as a refuge and stronghold long before the great brick-and-stone castles of the late Middle Ages. The rock above Lake Kernaala in Janakkala is impossibly steep on most sides, the kind of place where a small garrison can hold out against a much larger force simply because attacking is exhausting. Excavations show that the lower defensive constructions were mostly built of wood, while the works on the rock itself were of brick and stone. There was probably one tower. The castle was likely built at the end of the 13th century or in the very early 14th, and then abandoned at some point in the 1380s, leaving only foundations and the suggestion of walls.

The current name is not historical. It was borrowed from the nearby Hakoinen mansion, called Haga gard in Swedish. The fortress's original name has been lost. There is a strong possibility that what we now call Hakoinen was once called Tavastehus, the Castle of Hame, and that the name was later transferred to the larger fortification at modern Hameenlinna once Hakoinen had been abandoned. A document from 1625 calls Hakoinen 'the old Tauaste hus,' an explicit memory of an earlier name. The earliest mention of Tauestahus Castle in the historical record dates to 1308. If Hakoinen was indeed Tauestahus, then the famous Häme Castle at Hämeenlinna inherited not only its predecessor's purpose but also its name.

The 1311 raid recorded in the Novgorod Chronicle was part of the long, violent contest known as the Swedish-Novgorodian Wars, fought across what is now Finland and Karelia between the Catholic Swedish kingdom and the Orthodox merchant republic of Novgorod. The chronicle's passage is one of the few contemporary descriptions of what such an attack looked like from the attackers' side: 'The men of Novgorod went in war over sea to the country of the Germans, against the Finnish (Yem) people. And the Germans fell back into the citadel. For the place was very strong and firm, on a high rock, not having access from any side. And they sent with greeting, asking for peace, but the men of Novgorod did not grant peace, and they stood three days and three nights wasting the district.' Hakoinen fits the chronicler's geography. Whether the men inside the citadel were defenders we would recognize as Finns or as 'Germans,' that is, the Swedish-led colonial garrison of Catholic Christendom, is less certain than the chronicler made it sound.

Whatever happened in 1311, the castle survived as a working fortification for several more decades before being abandoned in the late 14th century. The castle rock then became part of a large estate belonging to the bailiff of Häme Castle, the same bailiff whose newer fortress was probably becoming the regional center of power. By the 15th century Hakoinen was simply farmland. Centuries later, in the 1840s, the artist Magnus von Wright illustrated the romantic ruin for the volume Finland framställdt i teckningar, edited by Zacharias Topelius and published 1845-1852. By then the site had become a piece of national landscape, an evocation of medieval Finland for a 19th-century Finnish nationalism still finding its footing.

Today there is a footpath up the hill, and the view from the top opens out across Lake Kernaala and the surrounding fields and forest of Janakkala. There are 3D panoramic reconstructions online for those who want to see what archaeologists believe the place looked like. On the ground, you mostly see lichen-covered stone, beech and birch leaves drifted in the cracks, and the occasional remnant of a foundation. It is not a dramatic ruin. It is a quiet hill that held something important for less than a century, then let it go. Whether it was the castle the Novgorodians failed to take in 1311 or only one of several candidates, the lake below it is the same lake that watched whatever happened. The rock has not moved.