City siting ranks among the most influential geographical decisions ever made by humans, dating back thousands of years and affecting billions of lives today. Yet it is a convoluted branch of inquiry, multivariate in its nature, replete with idiosyncrasy, and lacking a firm vocabulary. And because a city’s raison d’être changes over time—few people now move to Manhattan, for example, for its deep-draft harbor—original siting rationales oftentimes become archaic and, in retrospect, seemingly trivial.

Let’s start with New Orleans. La Nouvelle-Orléans was established by John Law’s Company of the West, backed by the French crown, for a dovetailing of commercial and imperial aims. The company hoped to enrich stockholders and the nation by creating vast tobacco and other commodity plantations, while the crown sought control over the Mississippi Valley before England or Spain made any further moves.

After nearly twenty prior years of French colonial settlements in Biloxi, Mobile, Natchitoches, and Natchez, both the Company and the crown came to realize that the colony’s headquarters needed to be on the lower Mississippi River, despite its hydrological vagaries and flood-prone banks. Soils there were extraordinarily fertile, and a strategic riverside perch would have defensive advantages. But where, exactly?

On September 9, 1717, the Company, according to its ledger, “resolved to establish, thirty leagues up the river, a burg which should be called New Orleans, where landing would be possible from either the river or Lake Pontchartrain.” That last clause implied various backswamp bayous used by indigenous tribes to circumvent of the shoal-prone mouth of the Mississippi as they moved between the interior and the coast. Specifically, Bayou St. John, and a connecting ridge known as Bayou Road, allowed for passage starting from Mobile or Biloxi and proceeding eastward through the Rigolets and into Lake Pontchartrain (really a bay), along the bayou portage, and to a particularly beautiful crescent of the Mississippi, fully ninety-five miles above its turbid mouth.

To be sure, waterlogged soils made all potential sites on this fluvial delta perfectly dicey for urbanization. But this particular place had less severe disadvantages and some key advantages, chief among that back-door alternative route to the sea. “I myself went to the spot, to choose the best site,” recalled city founder Jean-Baptiste Le Moyne, sieur de Bienville, on June 10, 1718, about ten weeks after his men began clearing the bank for what is now the French Quarter.

Thus, New Orleans was established in 1718 chiefly as foothold near the mouth of the great river to gain control of its hinterland, and sited on account of that key back-door bayou access. By 1794, that portage would be superseded by the Carondelet (Old Basin) Canal, now the Lafitte Greenway. Bayou Road today is a minor street through the Sixth and Seventh Wards, and Bayou St. John is mostly ornamental, but we’d have a different city in a different site were it not for these features.

We have a number of other “portage cities” in this nation. Niagara Falls, Buffalo, Detroit, and Sault Ste. Marie were all founded along short terrestrial linkages between the Great Lakes. Chicago is among the best examples, established at the point where the Chicago Portage connected the Mississippi Valley with the Great Lakes. A portage around the difficult-to-navigate Great Falls of the Ohio River gave rise to Louisville, Kentucky—comparable to Louisiana’s Alexandria, which is traceable to the impeding rapids on the Red River (hence Rapides Parish). Such spots are also known as break-of-bulk points, where humans in transit must disassemble their cargo and switch conveyances (raft to canoe, canoe to foot, etc.). Constant stoppages create demand for an inn, a restaurant, a supply shop, and other services, which calls for people to live there, which in turn calls for buildings to house them, farmers to feed them—and blacksmiths, and doctors, and banks, and churches. So grows a town, and perhaps a metropolis.

Cities also form at the head-of-navigation locations, above which vessels struggle to ply. Natchitoches, founded four years before New Orleans, marked the farthest point at which larger watercraft could venture up the Red River before encountering impassable logjams. After Captain Henry Shreve cleared those blockages in the 1830s, steamboats proceeded upriver, giving rise to Shreveport—and the relative decline of Natchitoches. At the national level, Minneapolis formed at the head-of-navigation on the Mississippi, as did Albany on the Hudson, despite that neither of these two cities depend heavily on river traffic today.

Similarly, some cities are on head-of-bay locations: Baltimore on the Chesapeake, Providence on Narragansett Bay, Tampa and Mobile on their eponymous bays, Lake Charles on Calcasieu Lake, and Madisonville on Lake Pontchartrain. Lafayette’s site derives from its position on a navigable portion of the Vermilion River up from the bay of the same name; for this reason, the city’s original name was Vermilionville.

Philadelphia took advantage of the fork of the Schuylkill and Delaware Rivers, while St. Louis is near the Missouri–Mississippi confluence and Cairo, Illinois, exploits the Ohio–Mississippi convergence. In Louisiana, Covington formed at the confluence of the Tchefuncte and Bogue Falaya Rivers; Donaldson sits at the divergence of Bayou Lafourche from the Mississippi; and French colonial Natchitoches benefitted from its proximity to the Camino Real connecting with Spanish Mexico. The point at which Bayou Sara disembogued into the Mississippi in cotton-growing West Feliciana Parish gave rise to the bustling little river port of Bayou Sara. But when Mississippi River floods wiped it out repeatedly, the community shifted “up the hill” to its loftier sister, St. Francisville.

As for train crossroads, Atlanta is probably the nation’s best example of a city traceable to nineteenth-century railroad crossings, and our own Slidell, while founded in the early 1800s, did not boom until the 1970s, after three modern interstates—I-10, I-12, and I-59—intersected there.

Cities are also sited for defensive reasons. Building Venice in a lagoon might seem like madness until one considers how the water would flummox invading Goths. So too clifftop communities like Monte Albán and Mesa Verde, which were all but impenetrable to attack. But once these defensive reasons became obsolete, other problems emerged: sinkage and rising seas in the case of Venice; lack of water and extreme inconvenience for the cliff dwellers. Colonial Louisiana had its own defensive outposts that succumbed to environmental conditions, such as Fort de la Boulaye in 1700 and the original site for Mobile in 1702.

Then we have Baton Rouge. This city originated from its elevated position on the Mississippi—the first true bluffs coming upriver—which benefitted additionally from being near the Bayou Manchac distributary, a site once suggested to host New Orleans itself. But Baton Rouge did not grow in importance until after 1848, when leaders decided to shift Louisiana’s capital from New Orleans, which had all the wealth and power (not to mention Dionysian distractions), to an interior site. In geography, these are known as forward-thrust capitals, state headquarters that are intentionally relocated from coastal to interior positions to encourage hinterland development. Baton Rouge is neither a perfect nor an explicit example of forward-thrust; the 1848 move came more as a result of an affluent rural planter lobby vis-à-vis their urban New Orleans colleagues, who came to realize they had, as the handlers of all that sugar and cotton, more of a stake in their country cousins’ argument than they had in a handful of government jobs. But the result was the same—the interior shift of political power—and it was matched by comparable moves regionally, such as Charleston to Columbia in South Carolina, Savannah to Atlanta in Georgia, Pensacola to Tallahassee in Florida, Mobile to Montgomery in Alabama, Natchez to Jackson in Mississippi, and Galveston to Austin in Texas.

New Orleans’ tricentennial offers a time to contemplate why Louisiana’s largest city was founded in 1718 and how we became the metropolis we are today. It’s also an opportunity to ponder where we are—how we could have ended up elsewhere, and how we might be different as a result.