Brielle is a fortress town. That's clear from the walls, ramparts, bastions and other fortifications surrounding the town. They were designed to protect the civil population from attacks from the outside. Various invaders have tried to conquer the Netherlands throughout the centuries.
Brielle did everything it could to keep these intruders out and that can still be seen today. However, the era of hermetically sealed town gates is long gone and the gunpowder fumes have long since evaporated. Thankfully, since now everyone can enjoy the beauty and charm of the fortress towns and their fortifications.
A number of fortress towns have joined forces to form the Association of Dutch Fortress Towns (Vereniging Nederlandse Vestingsteden). Brielle is a member of the association and sees it as a way of making known its fortress past.