Chalice could no longer manage this island alone. An extremely organized ambush within their base could not be coming from everyday pirates in the sea who just know how to find some treasures and rob people in the sea. After he fought with two powerful magicians, he realized that they were holding back to avoid revealing their true identities. Aside from that, he hadn't discovered any nearby vessel where they could have come from.
'Did they swim here?' Chalice absurdly thought but didn't entertain them since it shouldn't be possible to reach here through swimming with all their arrays and formation placed. For now, he had to further increase the defenses of this island especially now that their infrastructures were damaged due to the bombardments of the enemy. Some guards or magicians were even severely injured due to the chaos that has occurred outside.