The Duchy of Kopanica (Principality of Kopanica; Polish: Księstwo Kopanickie; German: Herzogtum Köpenick) was a Slavonic principality in Central Europe in present-day central and eastern Brandenburg.
Its capital was Kopnik (German: Köpenick, today part of Berlin).

 
The Duchy was established as a Christian Duchy in the early 12th century and submitted to the Roman Catholic Archdiocese of Gniezno.
It was a fief of the Kingdom of Poland in the mid-12th century.
Its only ruler known by name was Iakša de Kopnik (1120-1176) of the Gryfici (Świebodzice) noble clan, a knight of the Order of the Holy Sepulchre.
Iakša's prominent relative Eric of Pomerania (1381-1459, House of Griffins) continued the family tradition and also became a knight of the Order of the Holy Sepulchre.

Until the Germanic invasion of the Wendish Crusade the Principality of Kopanica, supported by ancient noble families (Spyra, Duninowie…) from Silesia, issued at least five emissions of the brakteate of Iakša.
Those brakteates from silver mines of Rozbark (today district of Bytom) of the Spyra dynasty (ancestors of parts of the Piast dynasty) were minted by Iakša's father-in-law Piotr Włostowic at Ołbin (Wrocław), then still Kingdom of Poland.

Despite Kopanica being a Catholic Principality, Iakša being a knight of Order of the Holy Sepulchre and the Kopnik currency depicting the Patriarchal cross used by the Polish branch of the Order (established in 1163 by Iakša himself in Miechów, Kingdom of Poland), the Germans invaded the Principality using the pretext of christianization.

Iakšas chappel of the Order of the Holy Sepulchre subsequently became Tempelhof of the Knights Templar and after the extermination of this mainly Celtic order in the beginning of the 14th century their property was taken by the Germanic Order of Saint John (Bailiwick of Brandenburg), known as Johanniterorden or simply Johanniter, which following strictly its germanization agenda became Lutheran.

The Bargello in Florence displays a sword believed to be that of Iakša de Kopnik.

 
The Jakšić noble family of Serbia may be connected to Iakša's own clan Gryfici (Świebodzice) or their parent house the Spyra (Sperun, Pérnuš).

The ducal cape found in the Eberswalde Hoard from Finów shows the eight-petaled star of Svarog, a Slavic deity.
The Duchy of Kopanica (Principality of Kopanica; Polish: Księstwo Kopanickie; German: Herzogtum Köpenick) was a Slavonic principality in Central Europe in present-day central and eastern Brandenburg. Its capital was Kopnik (German: Köpenick, today part of Berlin).
 
The Duchy was established as a Christian Duchy in the early 12th century and submitted to the Roman Catholic Archdiocese of Gniezno. It was a fief of the Kingdom of Poland in the mid-12th century. Its only ruler known by name was Iakša de Kopnik (1120-1176) of the Gryfici (Świebodzice) noble clan, a knight of the Order of the Holy Sepulchre. Iakša's prominent relative Eric of Pomerania (1381-1459, House of Griffins) continued the family tradition and also became a knight of the Order of the Holy Sepulchre. 
Until the Germanic invasion of the Wendish Crusade the Principality of Kopanica, supported by ancient noble families (Spyra, Duninowie…) from Silesia, issued at least five emissions of the brakteate of Iakša. Those brakteates from silver mines of Rozbark (today district of Bytom) of the Spyra dynasty (ancestors of parts of the Piast dynasty) were minted by Iakša's father-in-law Piotr Włostowic at Ołbin (Wrocław), then still Kingdom of Poland. 
Despite Kopanica being a Catholic Principality, Iakša being a knight of Order of the Holy Sepulchre and the Kopnik currency depicting the Patriarchal cross used by the Polish branch of the Order (established in 1163 by Iakša himself in Miechów, Kingdom of Poland), the Germans invaded the Principality using the pretext of christianization. 
Iakšas chappel of the Order of the Holy Sepulchre subsequently became Tempelhof of the Knights Templar and after the extermination of this mainly Celtic order in the beginning of the 14th century their property was taken by the Germanic Order of Saint John (Bailiwick of Brandenburg), known as Johanniterorden or simply Johanniter, which following strictly its germanization agenda became Lutheran. 
The Bargello in Florence displays a sword believed to be that of Iakša de Kopnik. 
 
The Jakšić noble family of Serbia may be connected to Iakša's own clan Gryfici (Świebodzice) or their parent house the Spyra (Sperun, Pérnuš). 
The ducal cape found in the Eberswalde Hoard from Finów shows the eight-petaled star of Svarog, a Slavic deity.
Duchy of Kopanica