The chapter begins by presenting a new origin story of secular time. This concept was developed in recognizable form in thirteenth-century scholastic angelological debates, where the terms saeculum or aevum came to denote an abstract and isochronic time independent of motion. Angels were cast as immutable mobiles, immaterial creatures moving through the created world without deterioration, and secular time was conceptualized in response to this imagined possibility of creatures ‘moving while at rest’. The second section of the chapter shows how Actor-Network Theory offers useful insights into how socio-technological networks centred on creating and sustaining immutable mobiles—to the degree that they are successful in this—thereby also mediate secular time. This provides the basis for the case studies presented in the following three chapters.