Final answer:
A rupture in western European attitudes toward ancient Roman culture occurred between the lives of Constantine and Theodosius, marked by the significant shift from ancient Roman polytheism to Christianity as the official state religion and the dramatic cultural, political, and religious transformations.
Step-by-step explanation:
Historians looking for a significant transformation in western European attitudes towards ancient Roman culture and traditions will most likely find it between the lives of Constantine and Theodosius. This period reflects profound cultural, political, and religious transformations that signified the transition from the ancient to the medieval world. Emperor Constantine not only established a new capital in Constantinople but also embraced Christianity, which dramatically changed the religious landscape of the Roman Empire. Theodosius carried these changes further by making Christianity the official state religion and thus condemning Roman polytheism.
The dissimilarities between the eras of Constantine and Theodosius exemplify the 'rupture' to which the question refers, particularly when contrasted with the influence of Charlemagne's attempts to revive Roman culture in the West, the establishment of the Pax Romana under Augustus, or the tumult of Nero's reign.