It's become a standing joke in my campaign (but I'm not laughing).

Goths invade. Goth army is massacred by city defenders. Goth family member runs at beginning of mass rout and cannot be caught by any pursuing unit.

Two annoyances to interject at this point:

1) Pursuing units should be faster than the pursued rabble.
2) Why do my pursuing units continue to stop and have a 'senior moment' just prior to actually catching the pursued rabble? Sometimes they continue on and sometimes they just stop.

To continue

Goth family member ends up retreated to a point 1000mi from home (across my empire) but when attacked by me next turn his guard unit is regenerated. Despite being surrounded by masses of my cav/inf, he fights his way clear and once clear of my troops he cannot be caught and so escapes to regenerate again.

Repeat ad infinitum.

An occasional escape when surrounded would be OK but this is ridiculous. At least if I had the chance to chase them down it would be better.