Iso Linnamäki is one of Finland's best-preserved medieval castle ruins. It was probably built in the late 1200s and abandoned before the Middle Ages came to an end. However, the history of the castle remains a mystery.
Gravel extraction, research and tourism
The history of Iso Linnamäki castle hill is linked to the early history of Porvoo, the key medieval town of eastern Uusimaa. Although scientists are intrigued by the history of the castle, much uncertainty remains about its history. Carbon-dated material found under the castle's foundations dates back to the Viking Age, around 800–900 AD. This means that the site was probably inhabited, but the castle itself is from a later period. No Viking Age objects have been found on the hill, but the abundance of medieval findings includes iron crossbow bolts, knives, pliers, a candlestick, nails and fragments of stone clay pots.
Some researchers assume that Linnamäki castle hill was built by the Danes at the turn of the 1100s and 1200s, while others link it to the campaigns fought by the Swedes in the Häme region in the 1230s and 1240s. The third possibility links the castle to the advance of the Swedes towards Karelia and the far reaches of the Gulf of Finland in the late 1200s.
In light of the latest major finding by researchers from St. Petersburg, the last of these interpretations seems the most plausible one. Archaeological excavations performed in 2007–2009 in the River Neva delta uncovered Landskrona castle, built by the Swedes around 1300. Its structure is almost identical to that of Iso Linnamäki. On the basis of the sensational discovery and dating of the ceramics found in Linnamäki hill, it can be presumed that, alongside the Vyborg and Landskrona castles, Linnamäki castle was a base from which the Swedish conquests of the east were launched in the 1200.
The castle may have been abandoned as early as the beginning of the 1300s but was possibly recommissioned, during the tumultuous period in the latter half of the century, as the administrative centre of the Porvoo bailiff district. It is certain, however, that – like many other small castles – Linnamäki was completely abandoned during the 1400s at the latest.
Linnamäki was also an important location in the modern era, as evidenced by objects discovered from the 1700s and 1800s, such as coins, fragments of clay pipes and glass bottles. The earliest map on which the castle is shown dates back to 1747.
The Russians took Finland from Sweden in the Great Northern War. In the summer of 1713, battles raged on both sides of the River Porvoonjoki bridge and the Russians had a gunpost strategically positioned above the city, on top of Iso Linnamäki castle hill. Stefan Löfving, who later became a famous guerilla fighter, burned the Porvoo Bridge during the battle. It is said that Linnamäki hill was still an artillery post as late as the Russo–Swedish War in 1741.
Gravel Extraction, Research and Tourism
Once the period of conflict around Linnamäki hill had ended, inhabitants of Porvoo began extracting gravel from the hill, and continued to do so despite several bans on this by the city authorities from 1756 onwards. Not even an Imperial Decree succeeded in ending this habit. Sand extraction has damaged the northern part and south-western side of the hill in particular.
The walls and moats of Linnamäki castle hill were restored in 1908–1909 as sand was hoisted on top of the wall from the bottoms of the moats. Archaeological excavations were performed from the latter half of the 1800s up to 1971.
Linnamäki castle hill has long been popular among sightseers. King Gustav III of Sweden visited the hill in summer 1789. The servants of the Porvoo vicarage were responsible for keeping the hill tidy. The hill's mysterious history, the well-preserved walls and the views from the top attracted both Porvoo residents and tourists from farther afield. Public festivals and events were arranged on the hill at the end of the 1800s.
The City of Porvoo and the National Board of Antiquities have been responsible for the management of Iso Linnamäki castle hill until this task was handed over to Metsähallitus Parks & Wildlife Finland and the City of Porvoo.