Bastille Day, the French national holiday, commemorates the storming of the Bastille, which took place on July 14, 1789 and marked the beginning of the French Revolution. The Bastille was a prison and a symbol of the absolute and arbitrary power of Louis the 16th’s Ancient Regime. By capturing this symbol, the people signaled that the king’s power was no longer absolute: power should be based on the Nation and be limited by a separation of powers.
Although the Bastille only held seven prisoners at the time of its capture, the storming of the prison was a symbol of liberty and the fight against oppression for all French citizens; like the Tricolore flag, it symbolized the Republic’s three ideals: Liberty, Equality, and Fraternity for all French citizens. It marked the end of absolute monarchy, the birth of the sovereign Nation, and, eventually, the creation of the (First) Republic, in 1792. Bastille Day was declared the French national holiday on July 6, 1880, on Benjamin Raspail’s recommendation, when the new Republic was firmly entrenched. Bastille Day has such a strong signification for the French because the holiday symbolizes the birth of the Republic.
Source: https://www.thoughtco.com/bastille-day-french-national-holiday-1368566