Built to keep the British out!:
Is it reasonable to have a town that is only accessible by sea?
It has been done "by design".
Akaroa in New Zealand was a town designed to be accessible almost solely by sea and to be extremely hard to access by land. When it was built Akaroa closely matched your specification.
While anything can be accessed by land given enough effort, Akaroa's location made it hard by the standards of the day, despite it being only about 100 miles from another major settlement that would have been deemed "potentially hostile".
Akaroa - designed to be inaccessible by land:------
In New Zealand (where I live) the settlement of Akaroa formed the original French foothold in NZ while the main British settlements were almost 1000 miles to the North. Nowadays Akaroa can be accessed by a charming long and winding drive through steep hill country. When first settled the same hill country provided a welcome buffer against unexpected access from the country's interior.
Wendy windy Google map route shows how hard Akaroa would have been to access.
A good feel for the sea based access can be gained even in modern photos
Guess where Akaroa is located ! :-).
If you were designing a world (hey, you are!) you could hardly imagine a more purpose designed "shield" for the distances involved. Akaroa is, of course, inside the long inlet. NZ's 3rd largest city Christchurch, is located beyond the "shield" where the right hand curving coast comes out to meet it.
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Many pioneer settlements that develop into towns in newly "discovered" countries only have sea access for practical purposes. Very early US settlements from Britain had no roads between them and what trails existed were initially unknown and totally dominated by largely hostile inhabitants who tended to take objection to be objects of discovery. (And still object to having been in many cases.) Overland routes were the domain of adventurers or expeditionary parties. The US was settled in numerous locations on both seabords long before a viable overland route was discovered.
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It's not a "city" per se but the East Cape is a large geographic area in New Zealand that for a long time was accessed very largely only by sea and only with difficulty by land. It had major settlements and industry which invariably used sea access for any movement of trade goods in and out. Even now it has "interesting" but usable rod access.
Sometimes even the modern road in is troublesome !!! :-)
Follow photostream for otrher photos of area.
The NZ "East Cape" was well known for its sheep rearing suitabilities. Up until about 1920+ all major produce from the area was brought out by boat over beautiful long wharves at Tolaga Bay and Tokamaru Bay. When the roads finally came the wharves died as commercial entities and are kept alive mainly for historical and recreational purposes. If you now image search for Tolaga Bay 90%+ of the images are of the wharf - a "dinosaur from the days of isolation.
- Tolaga Bay wharf, at 600 metres the longest on the coast, is no longer used by coastal shipping. The wharf took three years to build and was completed in 1929, but depression, war and better roads all took a toll and it closed to shipping in 1968. Since then walking the length of the wharf has been popular with both locals and visitors, some of whom also fish from it.
Even further out on East Cape is Tokomaru Bay -and another majestic wharf. - now derelict and dangerous at thje far end - but still lots of fun.
Also see Tokomaru Bay
- A century ago Tokomaru Bay was, believe it or not, a fairly major port, catering to over a hundred ships a year. It had a booming farming trade, a freezing works, a sawmill, a brick works, and a soft drink factory. All this industry went in and out by boat, with coasters ferrying the products up the coast to Auckland and dropping of supplies. The constant activity led to the formation of Tokomaru Bay’s own harbour board, and a greatly upgraded wharf – a 300m structure had rails embedded in the concrete for the small locomotive that ran the short distance from the freezing works to the port. Other facilities included the Te Puka Hotel (now Te Puka Tavern), a tennis club, a local newspaper, and two schools, and – after the war – a picture theatre.
By the 1960′s it seems as though only the hotel and one school was left, and the wharf and the shells of the factories are all that remain of the town’s season in the sun.