Why tf would the Saxons land NORTH of Hadrian's Wall?

This is the dumbest thing in the movie for me. I would have loved to have sat in on Movie Cerdic's war council.

Cerdic: The Plan is simple. We sail our massive fleet to scotland, and march our army south to Hadrian's wall.

Saxon 1:...Couldn't we just sail around?

Cerdic: Pardon?

Saxon 1: What I mean sir, is why are we taking the Roman garrison head on, when we couuld just...you know...take our ships and sail around the wall? Land our ships somewhere else, like somewhere that's not as formidably defended?

Cerdic: Why run from a fight? The roman's will just come south and fight us if we do that, so we'll take them head on.

Saxon 2: I don't think they will, sir.

Cerdic: Yuh-huh, why's that? *getting annoyed*

Saxon 2: Because the garrison on the wall is there to keep out the picts. If they diverted their force to resist our invasion behind the wall, the whole island would be left vulnerable to a pictish invasion from the north.

Saxon 3: Shut up, Cerdic know's what he's doing. We're landing in Pictland so we can ally ourselves with the Picts, promise them a share of plunder and land in return for their manpower and logistical support against our common foe, isn't that right, Cerdic?

Cerdic: Uhhhh....

Saxon 3: What is it?

Cerdic: ...I was basically planning to loot and burn the picts as well as the romans. Not even taking them as captivs or anything, i had it in my head to like...try to completely exterminate them.

Saxon 1: By Wotan, why the hel would you do that?!

Cerdic: Uhhhh...pure bloodlines?

The three saxons exchange significant glances.

Saxon 2: ...Aren't you worried that might unite the picts and romans against us?

Cerdic: Not really.

Saxon 3: Why would we want to start our conquest in the NORTH of england though? It's rainy, it's cold, it's sparsely populated-

Saxon 1: Yeah, like why don't we land somewhere in the south west of Briton, say just North of the Isle of Wight. You could call yourself the king of the West Saxons!

Saxon 2: King of Wessex, for short.

Cerdic: What kind of idiot would do that?

Saxon 1: The real Cerdic, for one.

Cerdic: Say what now?

Saxon 1: Cerdic of Wessex, the historical figure you're based on, landed his force in what is no Hampshire, which is about as far south as you can get of England.

Saxon 2: Why don't we just do that?

Cerdic: Because, idiots, if the romans found out about an invasion wouth of the wall they'd marshall the whole island against us and sweep us back into the sea.

Saxon 3: They didn't do that to Hengist and Horsa

Cerdic: Herschel and whonow?

The saxons look at eachother again

Saxon 1: You know...the actual first Germanic invaders of Britain, founded the kingdom of Kent about fifty years ago?

Cerdic: What year even is this? Didn't the opening voice over of the movie that lancelot did say the war with the Sarmations that forced the Knights to become Auxiliaries happen in 300AD?

Saxon 2: Well that would make *beep* all sense since the Roman power doesn't start phasing out of Britain until around 400 AD

Cerdic: Yeah well guess what, I'm Stelland Skarsgard and I do whatever the *beep* i want, and I say we take the most direct route and Land in scotland!

Saxon 1: But Scotland's not the most direct route, we're Germans. The closest part of britain to us is the southeast, Scotland is several hundred miles out of our way.

Cerdic stabs the first Saxon.

Cerdic: Anyone else want to chime in?

The saxons shake their heads

Cerdic: Excellent.