Speaking of security for large-scale events, at that time, the concept had not yet existed among nations.
That's not to say the world was at peace, with no villains daring to assassinate nobles under the heavens. As one of the oldest professions, assassins always thrived in the dark sides of history. Charlemagne assassins excelled in slashing throats with small knives, Albion assassins were skilled in using poison, Ymir assassins fell and rose in succession, Castile assassins were proficient in disguise, and the most famous were those under the Duchy's rule, the Camel Clan, from whom even the word "Assassin" originated. The only ones who were not adept at employing assassins were probably the original Habsburg family of Austria, who specifically provided assassination targets to assassins from various nations.