Christians have held diverse views towards violence and non-violence through time. Currently and historically there have been four views and practices within Christianity toward violence and war: non-resistance, Christian pacifism, just war, and preventive war (Holy war, e.g., the Crusades). The early church in the Roman empire adopted a nonviolent stance when it came to war since imitating Jesus's sacrificial life was preferable. The concept of "just war", whereby limited uses of war were considered acceptable originated with earlier non-Christian Roman and Greek thinkers such as Cicero and Plato. This theory was adapted later by Christian thinkers such as St Augustine, who like other Christians, borrowed much of the justification from Roman writers like Cicero and Roman Law. Even though "Just War" concept was widely accepted early on, warfare was not regarded as a virtuous activity and expressing concern for the salvation of those who killed enemies in battle, regardless of the cause for which they fought, was common. Concepts such as "Holy war", whereby fighting itself might be considered a penitential and spiritually meritorious act, did not emerge before the 11th century.