The Nomad Empires or Traction Empires were a series of empires that were constantly moving via traction fortresses. Initially these empires rose when Europe was still a maze of volcanoes and weather was unpredictable; being constantly on the move was an attractive option for many.
These empires triggered the Traction Era around 1 TE by motorizing their forts and wheeled houses. Before crude steam and internal combustion engines were used, slaves and/or horses were used to drag the houses across the ground. Some used pulley systems to move logs underneath these castles and houses to move them, a crane at the back picking up the logs and rolling them to the front (an extremely primitive cattipilar track system, basically).
The empires must have lasted for a thousand years or there abouts - they only motorized their homes around 1 TE, this period triggering the main bulk of the The Nomad Wars. This period lasted a further 400 years, ending when Nicola Quercus mobolized London into the first traction city.