The railway between Birmingham and Derby was authorized in 1836. George Stephenson was appointed chief engineer but was replaced by his son, Robert Stephenson, in 1837. The most challenging task was the 20 arch viaduct at Tamworth. The Birmingham & Derby line opened in 1839 but it was not a great financial success. Between 1841 and 1843 its dividend averaged only 1.8 per cent. In 1844 George Hudson organizing an amalgamation between the Birmingham & Derby, Midland Counties and the North Midland lines to form the Midland Railway.