A more thorough explanation:

Fetiales (also spelled feciales) were a group of priests in ancient Rome who were responsible for international relations and treaties. Their duties included declaring war and peace.

When Rome wanted to declare war on another nation, the fetiales would be sent to deliver a message and perform a ritual. This ritual involved throwing a spear into the enemy's territory to symbolize the start of the war.

Similarly, when Rome wanted to make peace with another nation, the fetiales would negotiate the terms of the treaty and perform a ritual to seal the agreement.

The examples illustrate how the fetiales were responsible for declaring war and peace and how they performed rituals to symbolize these actions. The fetiales were considered sacred and their persons were inviolate when they were on a mission to a hostile state, similar to how modern-day ambassadors and messengers under a flag of truce are protected. The fetiales were an important part of ancient Roman society and played a crucial role in maintaining international relations.