History of Koroistenniemi
In the 13th century, Koroistenniemi in Turku was Finland's most important secular and ecclesiastic centre, because in those days bishops controlled most of the secular administration as well as church affairs. The centre of the Diocese of Finland, the bishop's see, was moved from Nousiainen to Koroinen in accordance with a letter sent by Pope Gregory IX in 1229. There was activity in the area as early as during the Iron Age, but it is difficult to judge on the basis of the findings whether this was related to trade, settlement or a cemetery, or possibly all three. After the inauguration of the Turku Cathedral, the Bishop's see was transferred from Koroinen to Turku in 1300.
Koroistenniemi was a natural place for the Bishop's see at the time. The shores of the headland were steep, it was protected by water on three sides and merchant ships arriving from the sea could sail all the way to Koroistenniemi. An earth wall was built on the east side to protect the headland; access was possible across a bridge traversing the wall.
Excavations have uncovered the foundations of a 27.5 m long and 14.5 m wide church, with a narrower choir section made of stone at the eastern end of the main building. It has been suggested that the stone structure was part of a bishops' memorial chapel built in the 15th century, but doubt is cast on this by the fact that only one coin dating back to that time has been found during excavations. The foundations of an older, small church building have been found inside the large church foundation. The burnt layer found during the excavation suggests that the small building burned down.
Excavations have revealed the foundations of two stone buildings on the southern edge of the platform. The larger one is thought to have been the Bishop's palace and the smaller a defence tower. The foundations of a large oven between the two are thought to be the remains of a hypocaust, an ancient central heating oven.
Coin findings in excavations at Koroistenniemi are highly important to dating the use of the church. The majority of the 300 or so coins date back to a period between 1220s and the end of the 1300s, which is probably the period in which the church was used. According to some sources, the Victual Brothers, regarded as Baltic Sea pirates, burned the Koroinen church down in 1396.
More than 300 graves were found in Koroistenniemi during the excavations. The Christian graveyard on the site was used for around 200 years. Three graves are different than the others: they are made from bricks and located within the church structure. These are thought to be the final resting places of bishops Bero I, Ragvald I and Catullus. Other bishops of Koroistenniemi included Thomas, John I and Magnus I.
The excavations of the late 1880s to early 1900s revealed the significance of Koroistenniemi, prompting the State to expropriate the site in 1905. The ruins of the buildings were restored and protected, with the stone foundations left exposed so that the individual stones would not move from their current positions. A white cross was erected on the site of the ancient church in the early 1950s.
Over the years, the site has been managed by the Turku Historical Museum, the City of Turku Cultural Board and the National Board of Antiquities. In 2014, Metsähallitus took over the management of Koroistenniemi. All management is under the supervision of the National Board of Antiquities. The former pastureland is valuable for historical reasons and in terms of nature conservation, which is based on carefully timed mowing.
The house located to the east of the Koroistenniemi wall was occasionally used by the bishops even after the changes in 1300. The Koroinen estate was similar to the large manor houses in southwestern Finland.
Unlike almost all estates of the Bishop of Turku or the Cathedral, Koroinen remained in the Cathedral's possession after the Reformation in the 1500s, and was used by Lutheran bishops. Surrounded by a wall, the Koroistenniemi headland included the fields and pastures of the Koroinen estate after the Reformation. The Koroinen estate was transferred from the church to the State in 1932 and then to the City of Turku in 1985.