Did you know that Friedrichstraße, one of Berlin's main North-South roads, was part of an old trade route from Italy to the Baltic Sea? Together with today's Mehringdamm - until 1946 known as Tempelhofer Weg/Straße (Road to Tempelhof) and later as Belle-Alliance-Straße - it was used to transport goods to and back from the coast of the Baltic Sea.
Until approximately 1705 Friedrichstraße was called Querstraße (Transverse Street): that is because it actually cut through the main streets of the then new district, Dorotheenstadt (featured in our Berlin Calendar). The name “Friedrichstraße”, like the name of the whole new town which grew south of today’s Unter den Linden, honoured the first Prussian king, Friedrich I (formerly known as Kurfürst - Elector - Friedrich III).
The slightly older new district north of the boulevard, aptly named Neustadt (New Town), was later called Dorotheenstadt (after Great Elector's second wife, Dorothea, who owned the place).
Other streets were called Letzte Straße (Last Street), Mittelstraße (Middle Street) and Erste Straße (First Street). The latter is known as Unter den Linden today.
While Mittelstraße still exists, you won’t find Letzte Straße on Berlin maps anymore (none of them, in fact, as there were several). But the street itself is very much there: you know it as Dorotheenstraße.