<P> In the final third of the Spanish period, two massive fires burned the great majority of the city's buildings . The Great New Orleans Fire of 1788 destroyed 856 buildings in the city on Good Friday, March 21 of that year . In December 1794 another fire destroyed 212 buildings . After the fires, the city was rebuilt with bricks, replacing the simpler wooden buildings constructed in the early colonial period . Much of the 18th - century architecture still present in the French Quarter was built during this time, including three of the most impressive structures in New Orleans--St. Louis Cathedral, the Cabildo and the Presbytere . While the architecture from this period is commonly attributed to French influence, characteristics of the French Quarter, such as multi-storied buildings centered around inner courtyards, large arched doorways, and the use of decorative wrought - iron, were most ubiquitous in parts of Spain and the Spanish colonies . This influence may be attributed to the fact that the period of Spanish rule saw a great deal of immigration from all over the Atlantic, including Spain and the Canary Islands, and the Spanish colonies . In addition, although the architectural style of New Orleans, with its wrought iron balconies and full - height windows may remind one of Paris, many of New Orleans's oldest buildings actually predate the Haussman Projects that later renovated large areas of Paris in this same style . </P> <P> In 1795 and 1796, the sugar processing industry was first put upon a firm basis . The last twenty years of the 18th century were especially characterized by the growth of commerce on the Mississippi, and the development of those international interests, commercial and political, of which New Orleans was the center . Within the city, the Carondelet Canal, connecting the back of the city along the river levee with Lake Pontchartrain via Bayou St. John, opened in 1794, which was a boost to commerce . </P> <P> Through Pinckney's Treaty signed on October 27, 1795, Spain granted the United States "Right of Deposit" in New Orleans, allowing Americans to use the city's port facilities . </P> <P> In 1800 Spain and France signed the secret Treaty of San Ildefonso stipulating that Spain give Louisiana back to France, although it had to remain under Spanish control as long as France wished to postpone the transfer of power . There was another relevant treaty in 1801, the Treaty of Aranjuez, and later a royal bill issued by King Charles IV of Spain in 1802; these confirmed and finalized the retrocession of Spanish Louisiana to France . </P>

Which treaty gave the united states access to the mississippi river and new orleans for trade