 Complete the following phrase:  By the mid-16th century, Paris was defended by walls which had been built and rebuilt over the preceding centuries, but apart from the latest additions were largely obsolete for modern warfare and enclosed too small an area to contain the growing suburbs. In 1670, King Louis XIV ordered the demolition of all the walls surrounding Paris on the grounds that France was militarily secure and that a modern system of border fortifications had been constructed at great expense, and that like London and Madrid, Paris had become too large to fortify. Following the course of the demolished walls, the first boulevards were laid out, wide tree-lined avenues whose name is the French word for bulwark. An ambitious scheme of fortification for Paris proposed in 1689 by Frances leading military engineer, Marshal Sébastien Le Prestre de Vauban, was not proceeded with. Following the 