At the beginning of the 3rd century, the Roman Empire had enjoyed 200 years of internal peace and prosperity. Everything changed with the period of instability which started with the assassination of Severus Alexander in 235 and lasted until Diocletian's reign. During that 50-year period, at least 26 emperors were recognized by the Senate, the economy collapsed under hyperinflation and the loss of secure trade routes with barbarian invasions. A devastating plague struck, and ultimately the empire broke into three parts. In the turmoil, agriculture and manufacturing turned from regional specialization and long distance cash trade to production for local consumption and barter. Cities and towns fortified themselves. We will survey the course of this crisis and its resolution which allowed the empire to continue in the west for another two centuries.