Possible Clues:

• River which formed the boundary between Italy and Cisalpine Gaul
• Polish painting of holy figure in ancient boundary stream
• Polish hero the limit for Caesar?
• Polish trick to restrict current in ancient river
• Clean what could be venerated mosaic cross here with due care
• Once crossed, there's no going back
• Second river crossed in heading on — point of no return?
• Clean holy image in fateful stream
• Crossing point made famous by Caesar
• Point of no return; stream in northern Italy