When the knights of the Order came to later East Prussia, they brought heavy horses with them, which could carry armoured knights and pull wagons. The Old Prussians already resident there rode on "Schweiken", a small, wild horse-like breed. Consistent breeding of both of these together resulted in powerful but also very nimble warmblood horses in the 18th century. One of each breed was only ever paired off with each other within the respective breed.
Depending on the military or agricultural requirements, breeding sometimes tended more towards the nimble, sometimes more toward the strong type. Until the beginning of the 20th century, warmblood horses formed the backbone of East Prussian provincial horse breeding and the horses of the Prussian army. Due to increasing motorisation in the 20th century, they lost their significance as transport and draught animals. Today's Trakehners are almost exclusively used for riding and racing.
Illustration:
Prussian horse. Etching by Johann Elias Ridinger, around 1752.