*rei-

The core idea of this root (if it existed) was:

scratching, tearing, cutting

However, at least a branch of the family tree has focused on the resulting “trace” of scratching along something – that’s where the row and die Reihe are from.

According to the German etymological source that I am using (dwds.de), the root is also the origin of German reif and its English brothers ripe and reap. The idea here is that something is “ready to be cut off”.