@Leo80221 Megiddo was described like this in the light novel. Here's a quote from the light novel:
"Dancing, swirling rays of light rained down from the heavens, repeatedly reflecting and refracting near the ground and plunging through the knights before they could react.
There would be no opening bell to signal the beginning of the quiet massacre."
It is then further described in the novel. Rimuru is using the droplets that are closer to the ground as miniature lenses(that evaporate from the heat when the rays pass through them) to redirect in any direction Rimuru wants. Then Rimuru can also instantly make more of those droplets form where he needs them to be. The rays are literally rays of concentrated light as if through a magnifying glass, being congregated by tons of large lenses high in the sky, bringing them further down through more and more lenses. At which point the rays are sent in several directions, following the paths made by the small droplets.
As said by Razen, this isn't an actual magic attack that relies on magicules. The ray is 100% natural light, and light rays obviously move in straight lines.
Also, let's not forget the Anti-Magic Field barrier that Rimuru cast on the entire army, to stop the mages from finding ways to defend themselves from the light rays. As for the droplets, it's possible to use magic even within Anti-Magic Fields, but only if you're powerful enough. That's the entire reason why Rimuru could enter his city even when it had an anti-magic barrier on it that also blocks monsters from entering and leaving it(since they have tons of magicules in them).
I'm not sure how you envisioned Megiddo when you read the novel, but this is how it was described.