Exegesis:

The route indicated by this verse is difficult to understand (cf. commentaries in loc.), but the language itself is clear in its meaning as the text stands.

horiōn (cf. 5.17) ‘boundaries region.’

eis tēn thalassan tēs Galilaias (cf. 1.16) ‘to the Sea of Galilee.’

ana meson tōn horiōn Dekapoleōs ‘through the middle of the region of the Decapolis.’

ana meson ‘through’ or ‘within’; Moule suggests ‘right through.’

Dekapolis (cf. 5.30) ‘the Decapolis.’

Translation:

In some languages the combination of ‘returned’ and ‘went’ may be impossible. A possible adaptation may be ‘went back from the region of Tyre to the Lake of Galilee. In doing this he went through the region of Sidon and the region of the Ten Cities.’ (Note that Sidon is to the north of Tyre, and according to this description of the journey Jesus must have made a circuit to the north and then approached the Lake of Galilee from the east.)

Quoted with permission from Bratcher, Robert G. and Nida, Eugene A. A Handbook on the Gospel of Mark. (UBS Handbook Series). New York: UBS, 1961. For this and other handbooks for translators see here .