It is usually not possible to call any summons in Great Battles. We sometimes have events where we allow summons in Great Battles but that was not the case for the events we had recently. All the summons that were called in these events were called before the battles became Great Battles. A battle becomes a Great Battle as soon as there are at least 10 warriors on each side. If you don't want summons, make it a Great Battle as quicly as possible.