Schiltach, Kinzigtall, Schwarwald (D)

The width, length and favourable east-west direction in the middle and lower valley make the Kinzig valley important for infrastructure. The Romans maintained a road that traversed the valley. The Kinzigtalstrasse was a military road built under Emperor Vespasian in 73/74 AD from Offenburg through the Kinzig valley into the Roman Rottweil (Arae Flaviae) and on to Tuttlingen.
The main purpose of the road was to shorten the strategically important connection between Mainz and Augsburg. Until this road was built, the connection took troops via the Rhine bend at Basel and during the revolt of the (Dutch) Batavians in 69/70 AD, this had proved to be a problem. During construction of the road, several Castellae were built. In addition to Rottweil, the areas in Offenburg-Rammersweier, Offenburg-Zunsweier, Waldmössingen, Sulz and Geislingen-Haesenbühl, were augmented by part of the Alblimes fortifications in Frittlingen, Lautlingen and Burladingen-Hausen. All of them were located in Upper Germany except for Burladingen which was in Rhaetian territory.
The surprising discovery of the fortification in Frittlingen in 1992 only a few kilometers southeast of Rottweil shows that the Kinzigtalstrasse was secured and covered with a tight net of military fortifications. The suggestion that the Kinzig valley itself was home to another fortification has thus gained credibility. Again another fortification is assumed in Rottenburg.
Roughly at the same time that the Kinzigtalstrasse was built, Roman forts were constructed further north on the right side of the Rhine in places like Frankfurt, Heddernheim, Karben, Gross-Gerau, Gernsheim, Ladenburg (Lopodunum), Heidelberg and Baden-Baden (Aquae). Whether these were advanced posts or the Roman border between 73 and 98 AD, (following generally a defined line east of the Rhine), has yet to be determined.
In 98 AD, in the area of present day southwest Germany, the route between Odenwald and Neckar came under Roman control, making the connection from Mainz to Augsburg shorter yet. As a result, the Kinzigtalstrass lost superregional significance.
In present day Germany, the federal highway B 33 runs parallel to the Kinzig from Offenburg until it leaves the Kinzig in the upper valley to follow the Gutach towards Villingen-Schwenningen. From Hausach on towards Freudenstadt, the federal highway B 294, follows the upper Kinzig.

(Source : Wikipedia -> Kinzig)