I posted a query about Parthian army composition on the Strength and Honour FB group and had some really helpful responses, one of which was from Jim Webster, author of a superb guide to the Parthians for the Impetus rules. I have now downloaded a copy from Wargame Vault and am avidly reading through it to give me some ideas for the Strength and Honour army and for the Imperial Roman opposition, as the supplement covers both in detail. Thanks Jim!