The Coronation of Napoleon Bonaparte
The official day that Napoleon Bonaparte transitioned from his title as First Consul of France to 'His Imperial Majesty,' Napoleon I, Emperor of the French People. Prior to his coronation and 'election' as emperor of France, Napoleon had only held military or civil titles in the First French Republic, which still placed him below or above others within the same hierarchy. By openly styling himself as a monarch, the emperor of the French people no less, Napoleon put himself above all others and made clear who commanded the French.
In addition to the obvious importance the coronation had, its timing betrays how crucial Napoleon himself considered its completion to be. The coronation occurred only a year into the Napoleonic Wars, which would continue to rage on in various military theaters for the next decade. Napoleon saw his ascension to emperorship, to spend invaluable time away from his military conquests, to be more valuable at the time.
Unfortunately for Napoleon I, his spectacular coronation would not continue on for his descendants, as the House of Bonaparte would only last for two more monarchs whose achievements remained far short of the founder of their dynasty.