In 1690, Parat's flight had forced Costebelle to take power. The new commandant had to cope with some difficult problems. As well as some economic and disciplinary problems, he had to settle the question of the fortifications that were rendered necessary by the state of war. Following the English attack in February, Placentia no longer had one single defence worth calling a fort. Added to which, the enemy had taken away or destroyed most of the cannons in the colony. The officer realized that the settlement was in a precarious situation. In a memorandum, which is probably from him, the writer recommends the construction of a picket enclosure in the form of a palisade on one or other of the points of the gut, with a good battery of cannons, where all the inhabitants would be obliged to withdraw during the winter. This post would be maintained by two companies.

On September 8, 1690, without waiting for the king's answer to the memorandum that he is supposed to have written, Louis de Pastour de Costebelle assembled all the inhabitants of Placentia, Little Placentia and Point Verte to build an enclosure on the south bank of the gut. The work was completed within 15 days.

It measured 296 fathoms in circumference and was made of pointed pickets 7-1/2 feet high, strengthened by stays inside and outside and wooden cross-pieces nailed to the pickets. According to Costebelle, the construction could not last more than two years. Of the 100 men who were inside the enclosure during the winter, only 30 were armed; the remainder had iron-pointed sticks. At the time, the garrison consisted of 19 paid soldiers "sur le pied de 22," and the artillery at the rate of 12 francs.

Costebelle's construction was more threatening in appearance than really defensive. He wrote again on January 1, 1691 on the need to fortify the place:

Puisque ne le faisant pas, je puis vous faire voir que ce serait une perte tr6s considerable pour les n6gociants dans le commerce de la morue si les Anglais venaient a se saisir de Plaisance, ce qui fermerait le passage de Qu6bec aux vaisseaux qui y vont, la ruine de la p&che aux iles Saint-Pierre par les Malouins, et gC- n6ralement idour la cote de Terre-Neuve.

As a solution, he suggested fortifying the mouth of the gut, which was only 50 fathoms wide at low tide. Fort Louis was to be the answer to these problems.