Arthur considered himself ready. This battle, after all, was delayed for more than two years at least. His enemies were well prepared for him.
Just thinking about taking them out of surprise was out of the question. He knew they were well prepared and would never be allowed to take them by surprise this time.
So in times when surprise attacks wouldn't work, only brute and overwhelming strength would. He had already gathered his entire armies together. He learnt many techniques to suit this battle.
If all this wasn't enough, then he didn't know what else he should do. So once reached the lake city, he didn't delay or pause at all and went directly towards the sky.
When he reached high altitude, just above the clouds, he could see a faint luster taking the shape of a great sphere hanging midair. Its presence seemed to not stir anything around, making it look like it wasn't even there.