Richard
As I have got not experience whatsover in scripting I have copy edited your your script:

HTML Code:
script
declare_counter loop
set_counter loop 0
monitor_event FactionTurnStart FactionType sassanids

if I_SettlementOwner Dumatha = sassanids
console_command create_unit Dumatha "merc cata" 1
console_command create_unit Dumatha "merc veteranii" 1
end_if

if I_SettlementOwner Erewan = sassanids
console_command create_unit Erewan "elite cata" 1
end_if
terminate_monitor
end_monitor
while I_CompareCounter loop = 0
end_while
end_script
That works but despite press F1 button it only works once.When I remove terminate_monitor I get new units created on every turn.Could you kindly tell me what line needs to be change for the unit to be created only upon pressing F1.I guess that could be also way of having message appearing advising player he can get new units.Also is there a line that could replace "Sassanids" with something like "all except Romans"