Mid300s

Mid-300s is a historical label for the middle portion of the 4th century CE, roughly the years around 340 to 360, though some scholars extend the window slightly earlier or later.

During this period the Roman Empire was transitioning from Constantinian consolidation toward greater division and eventual separation of civil and military power. Constantius II was the dominant ruler occupying the eastern half of the empire; in the western provinces, rival leadership emerged when Magnentius seized the throne following the death of Constans, a conflict that ultimately ended with Constantius's reassertion of authority.

Religious policy continued to shape the empire; the Nicene Creed took prominence in church affairs, and Christian leadership gained political influence as bishops and provincial councils played a role in governance and policy.

Frontier pressure increased from the east with the Sasanian state and from the north with migrating or invading groups, foreshadowing the larger Gothic incursions that would intensify in the later 4th century and beyond. Urban administration and infrastructure persisted, supporting both military and religious institutions.

Historians use the term mid-300s as a shorthand for this transitional window; exact dating varies by source, and some scholars bracket the period as broadly as the mid-to-late 340s through the early 360s to fit different events or emperors.