He was present at the Lent Parliament of 1248, and we can hardly doubt that he shared in its bold rebuke of the king's misrule and its renewed demand for the appointment of the higher officers of state by the Council.

It was probably a sense of the danger of leaving at home such a centre of all efforts after reform that brought Henry to send him in the autumn of 1248 as Seneschal of Gascony to save for the Crown the last of its provinces over sea.
[Sidenote: Simon in Gascony] Threatened by France and by Navarre without as well as by revolt within, the loss of Gascony seemed close at hand; but in a few months the stern rule of the new Seneschal had quelled every open foe within or without its bounds.

To bring the province to order proved a longer and a harder task.
Its nobles were like the robber-nobles of the Rhine: "they rode the country by night," wrote the Earl, "like thieves, in parties of twenty or thirty or forty," and gathered in leagues against the Seneschal, who set himself to exact their dues to the Crown and to shield merchant and husbandman from their violence.

For four years Earl Simon steadily warred down these robber bands, storming castles where there was need, and bridling the wilder country with a chain of forts.

Hard as the task was, his real difficulty lay at home.