One of the most impressive of the animals painted on the walls of certain caves in Europe is the image of bos primigenius, the aurochs. This distant ancestor of the cow was awesome in both size and strength.
This photo is in public domain.
Although there was a measure of success with matching the appearance there has been much less success to date in reaching the awesome size of the Aurochs. A typical Heck bull should be at least 1.4 m (4'5") high and a cow 1.3 m (4'3"), with weight up to 600 kg (1,300 lb). Heck cattle are twenty to thirty centimeters shorter than the aurochs they were bred to resemble. The Heck bulls were not much larger than the bull of most breeds of domestic cattle, while wild aurochs bulls are believed to have often exceeded 1000 kilograms (2,200 lb), half the size of a rhinoceros. However, cross-breeding efforts continue to increase the size and weight of the breed, particularly in Germany.
Heck cattle. Wikipedia.
Modern efforts have been driven more by attempts to manage wild lands naturally with a full ecosystem of animals and predators. Ancient Europe had evolved with forests and steppes housing these animals and it is thought that they (or similar substitutes) would be valuable in natural management of the land.
Herd of Heck cattle in a park.
What strikes me as remarkable about this situation is that first there were the actual animals that our ancestors painted on the walls of caves, and then the rock art was used as the guide in an attempt to recreate the animals again - a marvelous example of life imitating art.
Sharon Levy, Once and Future Giants,Oxford University Press, New York, 2011.