Fort de Cavagnial (also known as Fort Cavagnolle, Fort Cavagnal, Post of the Missouri, or Fort de la Trinité) was a French fort and trading post located on the west cliffs of the Missouri River, somewhere north of Kansas City, Kansas, and Fort Leavenworth, Kansas, from 1744 until about 1764. While the ruins of the site were still visible when Meriwether Lewis and William Clark ventured in the area during their famed 1804 westward expedition, all traces of the fort were eventually lost by the mid-19th century. Today, the exact location of the fort is a mystery. History Active service The fort named for Louisiana Governor Marquis de Vaudreuil-Cavagnial, was the furthest west on the Missouri at the time. Its first commandant was François Coulon de Villiers who came from an illustrious New France military family. Like many frontier forts it doubled as a trading post operated by Joseph Athanase Trottier dit Desruisseaux (Joseph Deruisseau), who had a monopoly on trade on the Missouri from January 1, 1745 to May 20, 1750. Deruisseau chose the specific location of the fort because "the 'friendly Kansa[s] were a dependable source of high grade furs' and the location was strategic". According to the Kansas Historical Society, the fort was: small but substantial ... with a surrounding stockade of stout piles and with bastions at each of the four stockade corners. Internal buildings included a commandant's house, a guardhouse, a powder house, a trader's house, and a house for the trader's employees. The buildings were constructed of logs and most were covered with mud. Decline and abandonment The fort felt into decline sometime after the French and Indian War (1754–1763). During this time, the area in which Fort de Cavagnial came under the power of Spain, although French soldiers remained at the site of the fort until 1764, when Pierre-Joseph Neyon de Villiers (acting on behalf of Jean-Jacques Blaise d'Abbadie, the director-general of the Colony of Louisiana) ordered that the troops stationed in the area to "throw down" the outpost and retreat to New Orleans. Evidently, the site was not completely razed, for in 1804, Meriwether Lewis and William Clark stumbled across the old site during their westward expedition, noting in their journal that "[Fort de Cavagnial] may be recognised by some remains of chimneys, and the general outline of the fortification, as well as by the fine spring which supplied it with water."