Akila Apart City 
It leaves the Seine, climbs dead straight for a kilometre and a half to the Val-de-Grâce, then carries on south. Its line has not changed since the Romans laid it out. On that basis it is probably the oldest street in Paris still in use.
The cardo
Every Roman town is organised around two perpendicular axes: the east-west decumanus and the north-south cardo. In Lutetia the cardo maximus is this street. It crossed the Seine by a bridge to the island, ran through the lower town, then climbed the hill past the forum, roughly where rue Soufflot is now.
Southwards the road continued towards Orléans and Lyon. Northwards it crossed the Right Bank and headed for Senlis.
The street has kept the Roman alignment almost exactly. You can see it: it climbs straight, without a bend, in a quarter where everything else winds. Medieval streets go round things; Roman roads go through them.
Setting out for Compostela
From the eleventh century the pilgrimage to Santiago de Compostela in Galicia became one of the three great journeys of Christendom alongside Rome and Jerusalem. Four main routes crossed France. The one starting in Paris is the via Turonensis, the road through Tours.
Its gathering point is the Tour Saint-Jacques on the Right Bank, the last fragment of the church of Saint-Jacques-de-la-Boucherie, demolished at the Revolution. Pilgrims met there, received a blessing, then crossed the Seine and took this street south. Hence its name.
They left the city through the Porte Saint-Jacques, cut in Philippe Auguste's wall at about the level of today's rue Soufflot, and went on towards Orléans, Tours, Poitiers, Bordeaux and the Pyrenees.
The scallop shell, emblem of the pilgrimage, is still carved on a few façades in the quarter, and bronze studs marked with a shell now mark the pavement in places.
The street of books
In the fifteenth century printing reached France, and its first workshop opened at the Sorbonne in 1470. The trade spread at once through the surrounding streets, and rue Saint-Jacques became its centre.
For three centuries it held dozens of printers and booksellers, each identified by a painted sign: the Olive Tree, the Pelican, the Golden Galley. Those signs appear on the title pages of the period, with the line "rue Saint-Jacques, at the sign of…". It was the address of French publishing throughout the Ancien Régime.
The quarter was also the quarter of the colleges: teaching, books and students within the same hundred metres. The booksellers of boulevard Saint-Michel are the distant inheritance of that concentration.
Walking up it
Go from the bottom up, about twenty minutes.
- The foot of the street, facing the Petit-Pont, the Seine crossing used since antiquity and still in the same place.
- Saint-Séverin, slightly off to one side: flamboyant Gothic, with the famous twisted pillar in the ambulatory, one of the finest churches in Paris.
- The Musée de Cluny and the Roman baths, at the boulevard Saint-Germain corner.
- The Sorbonne, whose Richelieu chapel opens onto the street.
- Saint-Jacques-du-Haut-Pas, a seventeenth-century church carrying the street's name.
- The Val-de-Grâce, whose dome closes the view at the top.
The total rise is about sixty metres over a kilometre and a half. Little at a time, and a lot in the end.
Frequently asked questions
What is the oldest street in Paris?
It depends on the criterion. For age of line and continuity of use, rue Saint-Jacques, the Roman cardo maximus, is the strongest candidate.
Why is it called rue Saint-Jacques?
Because pilgrims bound for Santiago de Compostela took it to leave Paris southwards, after gathering at the Tour Saint-Jacques on the Right Bank.
Does the Camino still start in Paris?
Yes. The via Turonensis still begins symbolically at the Tour Saint-Jacques and walkers set out each year. Pavement markers signal the start.
Where was the Porte Saint-Jacques?
In Philippe Auguste's wall, at about the present junction with rue Soufflot. Nothing of it is visible above ground.