In 989, at the Council of Charroux, the Church proclaimed the Pax Dei, the "Peace of God," which declared clergy and other non-combatants "off limits" during military conflicts. Excommunication was the penalty for robbing a church, for robbing peasants of their goods or livestock, for striking or robbing a member of the clergy (unless he is bearing arms). Women and children were specifically added to the list of protected classes. In 1033, merchants and their wares were added to the list. A malefactor could avoid excommunication by making reparations.
This proved to be very popular in Western Europe. Local clergy had the responsibility to adopt and declare the Pax Dei in their region. The Abbey at Cluny gathered to itself a large territory, and many abbeys allied themselves to the Cluniac reforms. Once Cluny declared the Pax Dei, an enormous area was protected.
The Treuga Dei, or "Truce of God," was different. Created in Caen in Normandy in the 11th century, it declared that military hostilities could not take place on Sundays or any saints or feast days when daily work was suspended. Whereas the Pax Dei was declared locally by clergy, the Treuga Dei was universal. It was extended to Advent, Lent, and Rogation days (days of prayer and fasting). Over time, other days were added: Thursdays in memory of the Ascension, Fridays in memory of Good Friday, Saturdays because it was the day of the Resurrection. The Third Lateran Council in 1179 extended the Treuga to the entire Church.
How was this received by those inclined to wage war, and which influential churchman argued against the Treuga? Come back tomorrow and I'll tell you.