The mother country only seriously began taking measures to fortify Québec in the 18th century. Between 1700 and 1720, Québec played an important part in the colony's defence strategy. Throughout these years, France granted considerable sums of money to the city; nevertheless, internal conflicts undermined all good intentions. Although Québec was a vast site between 1700 and 1720, its defence system was incomplete and inadequate. The city was indeed a maze of temporary and permanent structures, isolated works, and entrenchments, all of which were the results of three different projects. The state of the defence system did not augur well for the colony; in 1721, the mother country refused to complete the fortifications. The Council of the Marine chose instead to fortify Montréal and Louisbourg. The former was located closer to the hinterland and its wealth of furs, and the latter's abundant fishing banks proved to be just as attractive.

In the next quarter century, the engineer Chaussegros de Léry proposed a series of projects to fortify Québec. Time and time again, his efforts were in vain. The new Minister of the Marine, Count de Maurepas, believed that the colony's defence policy should be based on the geographical and economical realities of North America. The Fortress of Louisbourg and the navigational difficulties created by the St. Lawrence River became Québec's bastion.

However, the fall of Louisbourg in 1745 triggered a state of panic among Québec's inhabitants. Governor Beauharnois, without awaiting approval from France, authorized that a new enceinte laden with masonry be built. These fortifications, modeled after Chaussegros de Léry's design, permanently closed the city at the end facing the countryside and integrated components of previous enceintes. However, the new enceinte was set up farther west that Beaucours' works (1693) and therefore allowed for the city to expand.

The project did have certain weaknesses. The flanks, for example, could be seen from some of the high grounds further west. Yet, it must be noted that the rampart was hastily built lest there be an imminent attack. This explains why Chaussegros de Léry, at the beginning of the 18th century, tried to join both old and new structures. During the siege of 1759, Montcalm and other French officers made harsh judgments on the fortifications. In some aspects, they were right; a part of the parapet and covered way had not been completed. On the other hand, criticism concerning the enceinte's adaptation to the terrain and geometrical layout was unfounded. The enceinte's weaknesses did not cause the 1759 surrender. Moreover, James Murray, who was in charge of defending Québec, used the rampart effectively when Lévis laid siege in 1760. Similarly, the existing enceinte discouraged the Americans from continuing their attacks on this front of the city.