The story below is a brief history of urban planning and transformation in Barcelona, Spain. It provides background and context for a five-part series about the city’s current comprehensive urban plan, which would reclaim more than half the streets now devoted to cars for mixed-use public spaces, or “superblocks.” You can find part one of that story here. This project was supported by the Kleinman Center for Energy Policy at the University of Pennsylvania, where the author, David Roberts, is a senior fellow.

Barcelona is in a perfect place for a city.

On the northeastern corner of the Iberian Peninsula, in the Spanish Levante, it sits on a plain of land about 5 kilometers wide, bounded by the Mediterranean Sea to the east, the Collserola mountains to the west, the Besòs river to the north, and the Llobregat river to the southwest.

It is a neatly defined and easily defensible area, with fertile soil, and it serves as the easiest passageway from the rest of the peninsula into Europe. Humans have been settling there, according to archeological remains, as far back as 5,000 BC.

The city’s origins trace back to the Romans, who settled in the area in 15 BC and, in the first century BC, built the medieval city of Barcino. It was small, surrounded by a wall roughly 1.5 kilometers in circumference, with the characteristic Roman grid of perpendicular streets.

In these modest beginnings are already visible two characteristics that would define Barcelona’s development over the years.

First, it began, and has always remained, a bounded and compressed city, dense from its founding. First physical walls and then the limits of geography have hemmed the city in and ensured that its residents are crammed tightly together.

And second, it has always been an intentional city, closely conceived and constructed by central planners. There have been very few periods of unplanned growth in Barcelona history. Unlike so many newer cities, it has not sprawled. Each new burst of growth has been on purpose; there has always been a plan.

Over the centuries, the city has been transformed again and again at the hands of visionaries, mostly notably architect Ildefons Cerdà, still considered one of history’s great urban planners.

Exploring that history can help illuminate the promise and perils that face Barcelona’s modern-day visionary, urban planner Salvador Rueda, who is now attempting to transform the city again, to prepare it for the coming rigors of climate change by making it less noisy, less polluted, and more walkable and sociable — all of which involves pushing back the tide of cars. (Read more about Rueda in part one of the five-part series on superblocks.)

Rueda’s plan would mean radical change — but Barcelona is used to that.

How Barcelona’s walls finally fell

After the Roman Empire fell in the fifth century CE, the years saw a series of conquests — Visigoths, Arabs, what have you — but they all reused the existing city.

In the Middle Ages, the city grew and became more complex, the center of a region known as Catalonia. An extended wall was built in 1260, and then in the 15th century, the wall was expanded again to encompass the new Raval neighborhood. The part of the plain outside the wall was used for agriculture to provision the city.

In 1714, Spanish King Philip V crushed a bid for Catalan independence. Barcelona surrendered and effectively became a colony, controlled from Madrid, heavily taxed, and continuously surveilled from the giant fortress citadel Philip built.

Remarkably, the wall around the city stayed in place — hemming in a growing population and almost completely separating the city from the sea next to it — for two more centuries. By the middle of the 19th century, population density was the highest in Spain, working conditions were miserable, sewage was out of control, water was dirty, and the city was struck by a series of cholera epidemics and riots.

By 1854, when the Spanish government finally gave permission to take the wall down, it was one of the most hated structures in Europe. Townspeople immediately went at it with crowbars and pickaxes; it took 12 years to completely remove it.

Then came one of the most extraordinary and underappreciated chapters in urban design history — a chapter that, though 175 years in the past, contains many omens and warnings for Barcelona’s current efforts.

Cerdà’s utopian plan for Barcelona

As soon as the wall’s demolition was announced, plans began for an expansion of the city. In 1855, the central Spanish government approved a plan by architect Ildefons Cerdà.

Cerdà is a legendary figure in urban planning circles, farsighted and progressive even by today’s standards. (Among other things, he is credited with coining the term urbanización.) Trained as a civil engineer, over time he developed a range of skills, from mapmaking to surveying to public health analysis. He was eventually involved in virtually every area of the city’s planning.

Cerdà was horrified by the conditions of the working class in Barcelona and set out to make his extension of the city — the Ensanche in Spanish, or in Catalan, as the district is still known today, the Eixample — a model of orderly, clean, safe, hygienic urban living.

Two things are worth noting about Cerdà’s plan.

First, he took what was, for the time, an exceptionally holistic view of urban quality. He wanted to ensure that each citizen had, on a per capita basis, enough water, clean air, sunlight, ventilation, and space. His blocks were oriented northwest to southeast to maximize daily sun exposure.

And second, his plan embodied what is — then and today — a striking egalitarianism. Each block (manzana) was to be of almost identical proportions, with buildings of regular height and spacing and a preponderance of green space. Commerce was to take place on the ground floor, the bourgeoisie were to live on the floor above (rather than in mansions at the edge of town), and the workers were slated for the upper floors. In this way, they would all share the same streets and public spaces, exposed to the same hygienic conditions, reducing social distance and inequality.

Each 20-square-block district was meant to be largely self-contained, with its own shops and civic facilities. Hospitals, parks, and plazas were to be spaced evenly throughout the city, to maximize equality of access.

Excluding the already developed Old Town and the two diagonal avenues intended to bisect the plain, the pattern of regular rectilinear blocks (exactly 113.3 by 113.3 meters, for 12,370 square meters, with at least 800 square meters for gardens) was to be replicated all the way to the borders of nearby settlements. The streets were to be wide enough to allow for the free flow of pedestrians, goods, and commerce (in the original plan, 35 meters wide).

In 1859, in response to criticisms, Cerdà released a modified version of the plan, with narrower streets no more than 20 to 30 meters wides and somewhat deeper buildings, with more room for commerce. The plan was approved by royal decree in 1860.

One of the plan’s most crucial and enduring features is its reliance on short, regular blocks. As the Romans knew, and city planners have since rediscovered, the hypodamic plan (or hippodamian, named after the ancient planner Miletus), with its short blocks and orthogonal streets, encourages walking, mixing, and vibrant street life.

A regular grid is comprehensible and easily navigable. There are multiple routes to any destination and regularly spaced choices. Because almost all streets are the same, it promotes the dispersion of foot traffic and street life.

Though Cerdà’s manzanas were (and are) criticized for their uniformity — the sameness is said to leave no room for great monuments or idiosyncratic artistry — it is just that underlying uniformity that has proven so endlessly adaptable.

The repeating structure of the blocks means that as social and economic circumstances change, old buildings can be shifted in use or ripped out, or multiple buildings combined. “You can change a building to introduce housing, a school, a hotel, or offices; you just need to put a building between two others that exist,” says Miguel Corominas Ayala, a professor at the Barcelona School of Architecture. “It’s very rigid geometrically, but it’s very flexible in use.”

Like Legos, the blocks have been built and rebuilt many times, for many different uses. (In the US, perhaps only Manhattan and Washington, DC, have similarly long experience with similarly regular blocks.)

Originally, each of Cerdà’s blocks was to have buildings on just two sides (sometimes three), occupying less than 50 percent of the total area, with the bulk of the interior space devoted to gardens and green space. The buildings were to be low enough (no more than 20 meters tall and 15 to 20 meters deep) to allow for almost continuous sunlight in the interiors during the day.

The goal was to combine the advantages of rural living (green space, fresh air and food, community) with the advantages of urban living (commerce, culture, free flow of goods and ideas).

Though Cerdà designed the city before automobiles, he included wide streets and his famous chamfered (45-degree) corners in anticipation of urban steam trams distributing goods and people. They would need lots of room to turn. (Seriously.) The design has, to Barcelona’s current dismay, proven extraordinarily accommodating to motor vehicles. Many of the areas created by the chamfered corners are now used for parking.

Along with his design, Cerdà also developed a strict set of economic principles and building bylaws governing the construction of the manzanas, to ensure that his vision was implemented. But when the Spanish government selected his plan in 1860, it did not ratify his principles and bylaws. That turned out to be significant.

Cerdà’s original design was a humanitarian marvel. If it had been built as conceived and survived to the present day, it would count among the world’s most progressive urban plans.

But that was not its fate. It was (eventually, mostly) implemented, but not as Cerdà envisioned. In fact, he was shunned by the city and his work fell into virtual obscurity.

What happened? The fate of Cerdà’s plan is a cautionary tale about the dangers that await Salvador Rueda’s.

Cerdà’s original plan fell victim to greed and politics

Though in many ways, Cerdà’s plan won in the end — its legacy is still clearly visible in Barcelona’s Eixample — it was compromised by commercial and political considerations from the outset.

In its initial form, it won approval from the (progressive) Spanish government and Barcelona city hall. But in 1856, a conservative shift in government led to the appointment of a new city council, which ignored the plan and held a competition to select its own plan.

Even as, in 1859, the royal government was approving Cerdà’s plan, the city government announced the winner: a plan by architect Antoni Rovira.