Complex sentence: The "Legio II Augusta", based at Exeter, was available, but its prefect, Poenius Postumus, declined to heed the call, but Suetonius was able to assemble a force of about ten thousand men.
Split into simpler sentences: The "Legio II Augusta", based at Exeter, was available, but its prefect, Poenius Postumus, declined to heed the call. Nonetheless, Suetonius was able to assemble a force of about ten thousand men.