In the autumn of 2010, a pair of local amateur archaeologists discovered a large medieval harbor area in the village of Ahvenkoski, which is presumed to be from the Viking Age or the Middle Age. The site is located at the mouth of the westernmost branch of the Kymi river, located on the eastern north shore of the Gulf of Finland. The findings included a smithy, a possible iron smelting furnace, forceps, ceramic pieces, as well as hundreds of iron objects such as boat rivets, similar to those found at Medieval and Viking Age settlements in different parts of the Baltic, Scandinavia, Scotland and Iceland.

    More recently, in August of 2012 in the same harbor area, a 2 x 3 meter wide Viking Age cremation grave was uncovered. Artifacts included a Viking battle axe, a knife, a fire striker and a bronze penannular buckle, all associated with burned human bones, melted bronze fragments and carbon crumbs. Before similar objects have been discovered in the Baltic Sea area and in Ladoga Karelia. Identical cape buckles have also been found in Gotland and similar axes in Lithuania and Denmark. A month before this, other Iron Age sites were discovered in the Viirankoski and Tesjoki valleys, by the same group in the area of Loviisa.

    Based on the findings, the Viirankoski site has been dated to periods ranging through the Pre-Roman Iron Age, Migration Period, the Merovingian Dynasty era and the Viking Age. Similar objects have been found in Sweden in the areas of Lake Mälaren, Birka and Göteborg, and also in the Danish Bornholm island. Several iron smelting furnaces, blacksmith's forceps, handmade ceramics and plenty of iron slag were uncovered at the site. According to scientists, the findings are exceptional and the Ahvenkoski grave can be considered the most significant Viking Age or Crusader period burial site discovered in the Gulf of Finland.

    Before these findings it was thought that the Finnish coastal side of the Gulf of Finland was completely uninhabited during the late Iron Age and Viking Age. When researchers of the Finnish National Board of Antiquities conducted their own survey of the area in 2005, nothing was found. Significant portions of both sites were destroyed by the construction of a new highway from Helsinki to Kotka, without conducting proper scientific research first. Later though, the Board of Antiquities made ”last-minute” rescue excavations, but only at the Ahvenkoski harbor forge. Based on further analysis by the University of Helsinki, the cremation grave was dated to the Viking Age in between 775 and 980 CE, based on their application of AMS (Accelerator Mass Spectrometry) techniques (Oinonen 2013) and through osteological analysis from burned human bone at the University of Helsinki (Salo 2013). Researchers also identified ceramic pieces from the Iron Age.

    Before the analysis, the local amateurs thought the site to be dated to the Viking Age at around 1000–1200 CE. In the autumn of 2014, the same group discovered strong archaeological evidence of a second Viking age cremation grave, from near the next branch of the Kymi river's estuary from Ahvenkoski to the east, in near Struka area of Pyhtää. The findings included a Viking sword pommel and guard with melted silver decoration, as well as riveted bronze plate fragments, possibly from a scale cup. In the opinion of the amateurs, two Viking Age graves and all the other results indicate, that it can not be coincidence and that it definitely shows the Vikings visited or lived in the region of the river and that the river estuary’s facilities were used from the Viking Age to the end of Middle Age, for as long as 600 years. It is also possible that the harbor could have been a part of the Gotland or Danish operating range during the Viking Age, and in fact, after the year 1200 it was used by Bishop Hemming for salmon fishing and as an export center.

    Between 2012–2014 a number of sites were located in the same area, not far from the Ahvenkoski harbor discoveries. In total as many as twenty possible Iron Age and Viking Age sites, of which closer examination was done in ten. Of those ten, as many as seven revealed evidence of what the amateurs interpret as early iron smelting furnaces and smithies. Two of those furnaces have been dated using AMS to between 204 BCE-180 CE, within the Roman Iron Age period. At five sites evidence was found of iron production in the early Iron Age, by elemental analysis in the University of Helsinki's laboratory of Chronology and by the local amateur group's own light microscope research.

    Some of the objects found also relate to the Migration Period and the possible Pre-Viking Age activity in the area, such as a cast bronze ”triangle legs buckle” from Nutanesi, which is the first artifact found from the Migration Period in the Kymi river valley. Other artifacts are from the Roman Iron Age and indicate a connection with Estonia and Scandinavia, like an extremely rare iron ”Bornholm belt buckle” from the Viirankoski site, dated to the Pre-Roman Iron Age of 500–300 BCE. Similar buckles have only been found on five different sites from Scandinavia, all located in Sweden and Denmark. One completely identical piece has been found on the island of Bornholm in Denmark.

    The local amateur archaeologists think, these discoveries dramatically changed the prevailing view about Iron Age and Viking Age activity in the eastern parts of the Gulf of Finland. Previous archaeological research, from since the 90s has not come to the similar result about activity in the Western Uusimaa region. These discoveries will change the view about Iron Age settlements on the eastern north shore of the Gulf of Finland, which until now was thought to be devoid of human settlement during that time period.

    The local amateur archaeologist group would like to thank in particular, the following researchers and institutions for all their help: Finnish Cultural Foundation Kymenlaakso Regional Fund (2013), The Swedish Cultural Foundation in Finland (2011 and 2014) and the researchers: Christian Carpelan, Mika Lavento, Yrjö Kaukiainen, Pirjo Uino, Timo Miettinen, Petro Pesonen, Henrik Asplund, Markus Hiekkanen, Kati Salo, Visa Immonen, Kristina Creutz, Simo Vanhatalo, Markku Oinonen, Pentti Zetterberg, Matti Saarnisto, Jouko Vanne, and Marika Mägi, Anders Tvauri, Aivar Kriiska and Valter Lang (Estonia), Charlotte Hedenstierna-Jonson and Gunnar Andersson (Sweden), Peter Pentz and Bodil Bundgaard Rasmussen (Denmark), Michael Buzinny (Ukraine), Tomasz Goslar (Poland) and Eleanor Blakelock (England).