The story
On 14 July 1789 a Paris crowd took the Bastille, a fortress prison holding seven inmates, for the gunpowder inside it. What mattered was not the prisoners but that the king's garrison had lost the city.
The holiday as fixed in 1880 is officially for the Fête de la Fédération of 1790, the first anniversary, rather than for the storming itself — a deliberate choice of the reconciliation over the riot.