 As noted early on by Thomas Aveling (later of Aveling & Porter fame), it was absurd to use four horses to pull a steam engine from job-to-job, when the engine possessed ten times the strength of the horses.It was therefore inevitable, once self-propelled traction engines had become sufficiently reliable, that they would take over the roles of many portable engines, and this indeed started to happen from the late 1860s.Other builders manufactured engines around the world.