Part of my trip to la Citadelle de Québec involved a visit to the Bastion du Roi, which features one of the oldest parts of the fortress: Cap aux Diamant Redoubt. A redoubt is a hardened fortification completely enclosed and separate from larger fortifications. Often it serves as a place of last retreat. In Québec, the redoubt is one of the surviving original French-era fortifications, albeit heavily modified by the British in the 19th century. These graphics illustrate some of those changes.
By 1783, the original French fortification existed outside the growing defensive works of the British. In this map, you can see the notably square shape of the redoubt as the pink square on the right side of the map near the cliff.
In 1823, the British decided to modify the square-shaped redoubt and undertook extensive modifications. The graphic below shows the original redoubt, the square, with the new plan, the hatched work.
The new plan simplified the structure.
But eventually, the redoubt was entirely enclosed by the growing fortifications. This shows its location in Bastion du Roi along with the construction of a block house to further fortify the bastion.
Credit for the piece goes to the designers of the various graphics.