Original: The Bastille originated as the Saint-Antoine gate, but from 1370 - 1383 this gate was extended to create a fortress to defend the east end of Paris and the Hôtel Saint-Pol royal palace.
Simplified: At first it was just the Saint-Antoine gate, but from 1370 - 1383, this gate was made bigger and became a fortress. It defended the east end of Paris and the Hôtel Saint-Pol royal palace.