Having read the book and dreamed up (and posted) a bit of a scenario it was time to give it a play through. Mark B took command of the Parthians.
Order of Battle
Special Rules
The table is bereft of terrain. The Roman deploys all of his forces first, then the Parthian.
The historical deployment would be a box formation (i.e. a square with the cavalry and allied troops in side), but the Roman is free to try a linear deployment if they wish (should they do so, the Parthian player is not restricted from deploying within 4H of the side edges). The use of aggressive deployment represents Crassus' desire to get into combat.
The aim is for the Romans to cross the table (at least half the force touching the Parthian table edge) and then to return and exit off their starting table edge.
The aim for the Parthians is to break the Roman army's morale. If the Romans break the Parthian army's morale they win (and the crossing the table aim is rendered obsolete).
Parthian units that evade off the table can return in a subsequent turn, provided the evade was from a charge declared by a Roman FP. The point of return can be anywhere on the table edge they exited from within a full move distance (i.e. 4H+2H).
All the Parthian CL are VBU 4 representing their plentiful supply of arrows.
The Game
The Romans in a box formation face massed Parthian horse archers.
The Romans advance into a hail of arrows.
Their precious skirmishers bravely withstand a charge.
Seeing that the Parthians are not trying to close round their flanks,
the Romans start to expand.
The Romans suffer their first lost unit,
but have routed a Parthian unit so all it's not all one way.
The Romans struggle to advance,
needing to halt to recover their order.
However they try some outflanking of their own.
Parthian cataphracts are readying for action,
as the Romans try desperately to press ahead.
The cataphracts are having a hard time of it,
but the Romans are continuing to suffer casualties.
The action appears to be on the wings.
Another Roman legion has been routed.
The cataphracts are being showered with javelins.
The Gallic cavalry is also suffering from missile fire.
The first horse archer unit has fled off table, but allowed to return.
(extreme top left hand corner is the "holding" box)
The Roman skirmishers have been routed.
Another horse archer unit has been destroyed,
but the Romans have lost their Gallic cavalry contingent.
Another two horse archer units left the table,
and critically the Parthian cataphracts along with their general have perished.
At this stage, if it wasn't for the optional rule to return units that have left the table,
the Parthian morale would have broken.
A fourth horse archer unit has left the table.
The Romans have just about reached the table edge, but can find no sign of any Parthian camp.
It is starting to look glum for the Romans as the Parthians have now swept round their left flank.
Time for the Romans to head back,
but oh dear,
their morale has broken.
Consideration
Making the Parthian horse archers all VBU 4 certainly improved the chance for them to inflict shooting casualties (roughly from a one in six to a one in three chance). It also meant that they had more chance of matching a Roman unit in combat especially after the Romans were disordered or had lost a casualty.
The returning after evading off table was suspect and I would not continue with that option. The Parthians should be able to make better use of the table space available.
The object for the Romans to cross the table needs a bit more thought as to what constitutes this being achieved. Perhaps all it requires is one Legion to make it before retreat is called.