The Bastille was a prison and fortress built in the 14th century to protect the eastern entrance of Paris. At the height of its use it held political prisoners, but by 1789 it was mostly empty except for stores such as gunpowder. Actually, the Bastille should be demolished and replaced by a city square. However, revolutionaries had other ideas – they wanted to get their hands on the gunpowder, so on July 14, 1789 they stormed the Bastille, losing about 100 people in the process. In the end, however, they won the day and proceeded to execute the governor of the Bastille and completely dismantle the building.
Interestingly, in France, they don’t even call it Bastille Day – they use it the National holiday or the 14th of July.