Attempts to domesticate zebras were largely unsuccessful. It is possible that having evolved under pressure from the many large predators of Africa, including early humans, they became more aggressive, thus making domestication more difficult. However, zebras have been trained and tamed throughout history. In Rome, zebras are recorded to have pulled chariots during gladiator games starting in the reign of Caracalla (198 to 217 AD). In the late 19th century, the zoologist Walter Rothschild trained some zebras to draw a carriage in England, which he drove to Buckingham Palace to demonstrate the tame character of zebras to the public. However, he did not ride on them as he realised that they were too small and aggressive. In the early 20th century, German colonial officers in German East Africa tried to use zebras for both driving and riding, with limited success.