Mapping History Underfoot
A methodology for discovering remnants of the ancient and medieval cities of Paris through open data and spatial data analysis tools.
Overview
Paris as a settlement has existed since the 1st century BCE, developing first from a Celtic tribal community to a Roman town, to a walled medieval city that expanded several times over, to a broad redevelopment in the 19th century. Despite these many reinventions, artifacts from even its earliest history are scattered in plain sight throughout the modern city. With the georeferencing and geoprocessing methodology used in this project, we see how layering historic cartography with archaeological data over the modern-day map of Paris can illuminate these tangible artifacts from the city’s founding through today and allow us to traverse history.
This is all possible due to efforts made regarding transparency and digital literacy by Paris' governmental and cultural institutions, underscoring the role of cities in preserving history and making it relevant through open source data and new technologies.
Background
Here's our map of modern-day Paris. The name of the city may conjure up images of the Eiffel Tower, quintessential blue-roofed architecture, broad boulevards, and the Louvre museum. But the modern Paris looks very different than it did for most of the city's existence.
We will walk through three eras in the development of Paris: Roman Lutetia, the Middle Ages, and the 19th century redevelopment of the urban plan under Napoleon III.
Roman Lutetia
50 BCE
Middle Ages
1000-1500
Redevelopment
Napoleon III and Haussman, circa 1850-1900.
Today
What we think of as the city of Paris today largely took shape in the 19th century under Napoleon III.
Evidence of settlement in Paris dates back to roughly 200 BCE, when the Parisii, a Celtic tribe, settled what is now “Ile de la Cité” in the center city, the island floating in the midst of the Seine River and where Notre Dame cathedral was built later in the 12th century.
The Romans conquered this tribe and took over in 50 BCE, founding their town on the left bank and hill (seen on the bottom half of the map).
From the Roman center of the left bank (purple), the Middle Ages saw the expansion of the city walls to include settlement on both banks (yellow), centering the Ile de la Cité once again.
This is Roman Lutetia circa 50 BCE.
A settlement on the center island, Ile de la Cité, is marked, as are the ancient Roman roads heading north and south.
Note the "Temple to Iris or Ceres" (even the mapmaker wasn't sure!) also illustrated and labeled on the left.
This is Paris in the late Middle Ages.
Specifically, this is Paris at the beginning of the reign of Charles VII, the year 1422, until the end of the reign of Henry II, in 1589.
As the city moved through the Middle Ages, it grew and expanded rapidly, but it also became more chaotic, crowded, and unsanitary. Note the winding and narrowing medieval streets on either side of the Seine River.
Haussman & Napoleon III
The solution to the crowding, proposed in the 1800s by then-king Napoleon III, was to hire architect Georges-Eugène Haussmann to overhaul the city's urban plan.
Haussmann implemented his vision via a huge redevelopment in the mid 19th century, incorporating Paris’ recognizable broad boulevards, arrondissements (neighborhoods), sanitation systems, the Opera House, and other major building projects.
In so doing, he also unceremoniously demolished much of the existing city’s street plan and structures and displaced roughly 350,000 Parisians. This historical map shows the city just before redevelopment.
Haussman & Napoleon III
The only part of the old medieval street plan that remained mostly untouched was a section of the 3rd and 4th arrondissements near the city center (in green).
Despite the widespread changes, remnants of the Roman and medieval settlements still remain today, as we will discover.
Haussman & Napoleon III
On right, a detailed view of new roads and construction that took place city-wide. Circled, the area that was spared most new construction.
“It's because of Haussmann's work that we have modern Paris. But, during the work thousands of low-income Parisians were forced out of their homes and relocated to Belleville and elsewhere in the Paris suburbs. Neighborhoods that had existed for hundreds of years were destroyed by the new, broad boulevards. On any modern map of Paris it's easy to identify Haussmann's work. The straight, wide streets, the Grands Boulevards — Boulevard St Michel, Boulevard de Montparnasse, Boulevard Haussmann — that slice across an older plan remind us that he was the architect of modern Paris.” - Paris Insider’s Guide
Mapping Historic Cities: Georeferencing
The Paris that we think of today is a mostly Haussman-era design. As you can see, layering the Haussman-era map from 1868 matches the modern Paris urban plan almost exactly. In this example, almost all of the streets from the historical map line up perfectly with our current map of the city, so there is little to no skew of the illustrated historical map.
Georeferencing the 1868 map, drafted mid-Haussman construction.
Even though Haussman broadly destroyed much of the old city, we can use our historic maps and spatial data analysis to "rediscover" remnants of it.
The process of placing an illustrated map over modern geographies, and tying the map image's raster data to real Earth coordinates, is called georeferencing . A georeferenced historical map or image often requires "shifting, rotating, scaling, skewing, and in some cases warping, rubber sheeting, or orthorectifying" the data being georeferenced (Esri GIS Dictionary, 2023).
While the 19th century maps are easily georeferenced because of their similarities, the Roman and medieval historic maps require additional research to place them, based on often sparse information available in these maps. We then process the map data using spatial analysis tools in order to accurately match it to the modern geography of a base map.
Sometimes, the mapmakers' drawings of the old cities were surprisingly accurate. Other times, the maps must skew to fit features on our current map of the city.
Starting with three historic maps: 1) Early Roman Lutetia (50 BCE), 2) Paris in the Late Middle Ages (15th century), and 3) Paris under Napoleon III (mid 19th century).
Georeferencing Process
First, we identify and download detailed historical maps from open resources. In this case, I used Gallica (the National Library of France's digital archives) and Wikimedia Commons. I was looking for maps with enough detail to allow for the marking of specific control points (street corners, buildings, and other key landmark points) that would line up exactly with points on the modern map.
Once the map is placed over the base map, we can manipulate it manually to get an estimated placement, then add at least 3-4 control points at various edges of the historical map in order to accurately match it with the base map layer beneath it.
Results
Once we have georeferenced data from a map, we can approximate the boundaries of those older settlements and hypothesize where artifacts and ruins of the old cities might lie in the current city boundaries. Below, the resulting georeferenced maps of Roman Lutetia and late medieval Paris.
Georeferenced map of 50BCE Lutetia (Roman Paris) at its founding.
Georeferenced map of Paris in the 15th century, the late Middle Ages.
Applying Hot Spot Analysis
Layering Archaeology
To dig deeper into the city's history, we can layer both geospatial archaeological repository data and protected buildings data from Paris Open Data's digital archives.
Here again is all of our archaeological data, filtered to include just those artifacts from Antiquity and the Middle Ages. The triangles show all the archaeological discoveries from Antiquity and the Middle Ages within the current Paris city limits.
Black triangles represent findings from Antiquity (the period of Western Civilization before the Middle Ages that includes Roman and Greek expansion); Red from the Middle Ages. Blue shapes highlight historic buildings.
We can start to see a pattern of clustering forming, but we need to apply spatial statistics to know more.
Exploring Artifacts "on" the Historical Maps
First, I decided to explore some of the archaeological findings to see what I could discover from the various layers of data.
I was interested to know what happened to the ancient "Temple of Isis or Ceres" marked in the 50BCE map of Roman Lutetia. From my resesrch, I found that the existing Church of Saint-Germain des Pres was said to be built over it.
We can both locate the church on the current basemap (green label). Not too far from the mapmaker's approximation of the Temple. Then, we can click on nearby archaeological finds (black triangles) to see what pops up from the era of Antiquity.
This reveals a series of Roman burial sites were discovered just nearby. Was this part of the temple grounds? An area for further research; but already we're starting to make links between the data layers.
Finding Roman Lutetia Along Ancient Roads
Doing some more research within the dataset and generally, I was able to locate some more well-known artifacts from the Roman settlement in both the historical maps and the archaeological dataset.
Note the long yellow line. This is Rue Saint-Jacques, the oldest road in Paris and the Roman's primary road through Lutetia. the basis for the grid layout of the rest of the city. This makes sense, since we know Romans settled on the hill in the south part of the city, or Paris' current Left Bank.
In the map, I manually marked some of these key archaeological discoveries.
In yellow, Roman "cardos," or main roads (now functioning streets: Blvd Saint-Michel, Rue Saint-Jacques, and Rue Mouffetard).
From the top, purple pins indicate: Rue de la Colombe, remnants of the old Roman settlement walls; Notre Dame Cathedral, which stands overtop a Roman crypt; Thermes de Cluny, the Roman Baths found under the Cluny Museum; Arenes de Lutece, the Roman Forum; An ancient Roman necropolis (50 burial sites discovered).
Zooming in on Antiquity (and the Romans)
Using spatial statistics, we can filter for the era of an artifact's discovery and confirm the hot spots for archaeological finds from that era. Kernel Density Analysis will give us a clustering trend, but Hot Spot Analysis gives us statistically significant clusters. On the right, a Hot Spot Analysis of findings from Antiquity. Read more about Hot Spots in ArcGIS here .
Darker purple areas show us the statistically strongest hot spot areas for ruins from this era.
Just where we'd imagine it to be, based on what we've learned of Roman Lutetia. Neat, right?
Zooming in on the Middle Ages
Next, looking at our historic map from the 15th century, we can clearly trace the old medieval city's protective walls in the map.
The clustering of archaeological finds from this era, in red, appears to move from the Left Bank into a more central location within those walls.
Applying hot spot analysis again to this data, we see that that the hot spot areas do tend to move northwards, and do cluster within the bounds of where we know the old medieval walls to be.
Again, darker purple areas show us the statistically strongest hot spot areas for artifacts from this era.
Roman & Medieval Paris Today
The map tour below shows more locations of significant remnants and discoveries from both Roman and medieval Paris that can be found in the modern city.
Two of the most important ancient Roman ruins in the city, the old forum (Arènes de Lutèce, illustrated right) and Roman baths (Thermes de Cluny), can still be found in central Paris.
Arenes de Lutece
Roman Baths & Hotel de Cluny
Notre Dame Cathedral
Medieval City Walls
Medieval Palace & Prison
Roman Necropolis
Roman Cardo Maximus
Arenes de Lutece
The old Roman forum lies in the aptly-named Latin quarter (fifth arrondissment). The forum once seated 15,000 people and also was used as an amphitheater for gladiatorial combats.
Roman Baths & Hotel de Cluny
The baths lie under/within the current Cluny Museum, a museum dedicated to the Middle Ages also found in the Latin quarter.
Rue de la Colombe: Remnants of the Roman walls
Notre Dame Cathedral
Notre Dame Cathedral is truly a centerpiece for all of this data. Beneath its front atrium lies a Roman crypt. Its original walls were constructed in the Middle Ages between 1163 to 1272, after more than 100 years of work. It was reconstructed and expanded in the 19th century, when "gargoyles, chimeras and other fantastical statues" were added alongside the notable spire. Much of this was saved despite a huge fire in 2019, in the middle of its 850-year reconstruction. It remains a major centerpiece of the city, hosting artifacts from even the earliest settlement.
Medieval City Walls
The medieval walls are still being excavated and encompass several different enclosures erected over the Middle Ages. One of the earliest enclosures is from the 11th century, and new remnants have been discovered along Rue de Rivoli .
Medieval Palace & Prison
Conciergerie, home of medieval royalty, was transformed into a prison in the 4th century, and the kings and queens moved into the Louvre palace.
Roman Cardo Maximus
Rue Saint-Jacques was the primary road through the Roman settlement, and the basis for the grid layout of the rest of the town.
Why Does This Matter?
While none of this data is novel or surprising (in fact it's been analyzed already in various ways), hopefully this methodology demonstrates a role that cultural institutions and data analysts can take on together in making the past relevant today through new technologies.
Paris in particular is a model city for this type of analysis, allowing us to visit these sites virtually and discover new insights about the city's urban plan and evolution without ever leaving our desks, thanks to their extensive efforts to publish open datasets via cultural and governmental organizations. (Though, if you do have the chance to leave your desk and go to Paris, I recommend you do!)
With this data, geospatial analysis tools allow us to uncover traces of ancient and medieval history in the modern day city and visualize the changes that made the modern Paris. This type of hands on illustration could be a useful tool for educators, historians, policy makers, preservationists, museums, and more.
What could be next for this analysis?
Because this map was originally designed and processed in ArcGIS Pro (the desktop software) then transferred to ArcGIS Online, I would next spend some more time tweaking and editing the Web Map in ArcGIS Online and pulling 1-2 more georeferenced images from ArcGIS Pro. Web Maps do not currently support georeferencing, so I had to recreate these images using geotiffs. One additional dataset that I had less time to display and analyze was the Protected Buildings dataset; I'd like to cross-reference some of those sites with the hot spot analyses in this map.
Beyond that, there are so many ways to further layer and analyze data in a map like this. Two ideas I had were to 1) geocode and visualize responses from the city's recent survey, "Which Paris in 2030?," which asks about the public's ideas for future urban development, and 2) to write and integrate a Python script to pull in images to each of the artifact pop-ups from Gallica or other Open Data France resources.
Methodology & Materials
- Online research
- Data collection (Python, Open Data France/Paris, Wikimedia Commons)
- Spatial data analysis (ArcGIS Pro)
- Georeferencing
- Geocoding and geoprocessing
- Spatial statistics: Hot Spot Analysis, Kernel Density
- Map design (ArcGIS Pro)
- Storymap creation (ArcGIS Online)
Explore the Full Map
Mapping History in Paris Web Map Reconstruction
