Slitherine

depends who is up on the hill. Whoever is at the higher elevation gets a + POA
In the case of a gully the same holds true the guys on ground level are above the lower level in the gully so the guys at ground level are higher and get the +POA

Vercingetorix is getting an advantage for being uphill.

Romans are very disordered reducing them to 2 dice. They have 2 POA's Swordsman & Flank
Gauls are very disordered and I assume overlapped or have casulaties reducing them to 1 dice. They have 1 POA for uphill.

The Net POA is +1 to the Romans, so it is shown as a +. Without the uphill the Romans would be ++

Which means the romans rolled 2 dice needing 4,5 or 6 to score a hit whilst the gauls needed 5 or 6 to score a hit on their 1 die. Looks like poor rolls for you & a good one for your opponent.

Had the hill not been a factor it would have been anything but 1's or 2's for you to score a hit.

If your romans were superior they would have rerolled any 1's and if elite any 1's or 2's. However that is still not a guarantee of success - I've seen plenty of combats were a 1 or 2 gets rerolled as a 1 or 2!