Fetials (fetiales) were a twenty-member college of priests dedicated to Jupiter. Priests were elected for life. Their task was to declare war and conclude an alliance, which was associated with special magical formulas. Their activities were closely related to religious rites and surrounded by the highest secrecy.
When a diplomatic mission was organized, fetials chose one of them, called pater patratus. He went to the border in his priestly robe, with a sceptre in his hand and with a flint, which was the symbol of Jupiter as the god of oaths, and in the company of another fecial, who carried a handful of grass uprooted from the Capitol Hill. If the matter was settled peacefully, i.e. the country submitted to Rome, then after returning, appropriate prayers were said in the temple of Jupiter and peace was solemnly announced. The text of the system was read during a service combined with an offering to Jupiter. When the conflict could not be resolved peacefully, pater patratus would go to the frontier and throw a charred and blood-soaked dogwood spear into enemy territory.
Interestingly, when Rome expanded its borders to such an extent that it was difficult for special emissaries to go to the borders with hostile countries, it was considered that a fragment of land near the temple of Bellona is non-Roman and the rite of declaring war was practised there.