Also, the question is unclear. Why should it be surrounded?

well isnt it ancient though?

just to make it clear that i ask about ancient town or village, for why i ask why it should be surrounded ? well isnt it weird ? to purposely not build defensive wall there ? if enemy ship manage to pass through, they basically have no defensive wall to defense against enemy and that outer wall become useless since enemy already get inside without even needing siege engine, sorry for my bad grammar or english.

oh yeah also although in that image it show a wall that pass through the sea or water(i know it not enclosed for ship movement and thats not the wall i asking about, nor i see any problem with that wall, just to make it clear), and atleast have more defensive capability against enemy ship from what i see some even dont have that kind of wall or just made of plank.

Trying to pass an enemy ship through a stranglehold like the one in the image you posted is nothing short of suicidal. Even if a ship happened to pass through without burning or worse, defendants on the beach would be awaiting the crew with spears lined up.

You might consider why there are gates in the landward side of a defensive wall. Usually the purpose is to control access without cutting it off completely. Chains were often used to control harbour access. A dam through the water has drawbacks - expensive to build, changes water flow in the port, etc. Probably someone knowedgeable on fortifications can be more specific and comprehensive.

i guess i need to photoshop a bit to show the problem i guess since that not the wall i ask about, and as i say " from what i see some even dont have that kind of wall or just made of plank."

also i dont think that tag is right though since it also mostly exist in viking era and some medieval era should i add back that two tag ?

medieval mostly viking era but the tag about ancient history is not add by me i just notice it, although i think there some similar town or village like that. so should that tag removed ?

I'm guessing the ancient history tag was added in direct response to your comment that "i ask about ancient town or village". It's very difficult to frame an answer when the scope of the question changes.

well in my opinion medieval is ancient though, and seems like the early comment that say or ask something like medieval is not ancient get removed. my original tag is medieval and viking.

Do not reply in comments. Edit the question.

I'm voting to close this question as off-topic because it is hypothetical, not history.

what part of it is hypothetical ?

The sea is historically as good or better than a wall for defensive purposes. Building an additional wall inside the harbour would have been cost prohibitive.

@semaphore can you elaborate more why the sea is good for defense and why it cost prohibitive ? thanks

Because historically few people were able to swim, and those who could would be helplessly exposed to the defender's missile troops while trying to reach the shore. Walls are costly to build; in your example they already have walls extending into the sea, so a second layer of walls on the beach would've been a waste of money.

but wont it vulnerable against ship ? (excluding walls extending into the sea, because there some village or town that dont have that, as i already mention) if the ship manage to land, even if the unit use row ship they probably use the reserve unit to engage so i doubt fatigue would be major point and using the defender to engage the landing troop make the outer defense wall pointless and risky, why leaving that backdoor open like that ? there must be a reason. also if they have second layer at least even if the enemy use ship they also need to bring siege engine too.

#lijun - allow me to repeat my plea - please don't reply in comments. Long comment strings like this diminish the value of H:SE.

What is the point of a seaward wall? Walls help to defend against infantry. There is no chance of an infantry attack from the sea. Attacks from the sea are by ship, and the response to a maritime attack is either shore batteries or ships.

Building a wall on the seaward side is going to be very inconvenient for the inhabitants of the city and add zero to the defense.

Ships don't care about walls -walls are on land, and ships are at sea. The wall doesn't discourage or affect the ship.

i mean ship that carry troop that can landing into the city, example the viking, which i found mostly their port dont have wall defense facing the shore ( as i say excluding the seaward wall here, i edit to include some example of port city that i found without that, i hope this can clear up some misconception here) sorry cant help in this reply since many get misconception in my question.

The defense against a marine landing is to sink the ship - walls won't help.

Depending on the era you can either fight the incoming ship with ships or with shore batteries. Marine landings are very tough, almost impossible. Suggest you research marine landings.

I think you need to revise teh question to clarify your assumptions and to document your assumptions with research. Then it can be considrered for re-open.