I’ve got a fantasy world in which the landmass is essentially a large series of archipelagos and island chains. For a real world comparison, think the Hawaiian islands in range of size and distance from island to island. For their early history, these islanders travelled to and fro for commerce and war in boats of various sizes and types. Later, however, an empire emerged that linked the nearby islands with a series of titanic bridges.

For the purposes of the question, don’t worry about the possibility of building these bridges; magic is in place that makes the work possible, but not easy. The question remains, why would this empire choose to put massive work in to build these bridges when a rich shipbuilding culture exists? In case it is relevant, the empire in question has approximately Antonine Rome's technology, besides the magic, and is expanding in order to add strategic resources like iron and horses to its collection.

closed as primarily opinion-based by Mołot, elemtilas, Frostfyre, JohnWDailey, rek Oct 16 at 1:07

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 20
    why did we build the brooklyn bridge when ferries existed, simple you can move more stuff and do it much faster on a bridge than a boat. – John Oct 15 at 5:43
  • 2
    Storms? Changing winds from season to season? Strong currents? Volcanic islands with too abrupt coast-line? Reefs only a few sailors know how to avoid? Not needing to maintain ports for ships? Not paying taxes to use those ports? – Alberto Yagos Oct 15 at 5:45
  • 2
    @AlbertoYagos - Good points, however - taxation is arbitrary. A state can invoke taxes on anything it wants, including bridges. – Battle Oct 15 at 7:25
  • 2
    Have you think of anything that's stopping them from building a bridge? – Mr.J Oct 15 at 8:04
  • 3
    Why do you want/need bridges in your world? Assuming you don't create a world randomly, you might have an idea why you want them. Please elaborate. – Raditz_35 Oct 15 at 8:22

For the same reason why the British filled in the Braye du Valle in Guernsey in the Channel Islands. its a lot easier to defend

Historical Example: the Braye du Valle

The Channel Island of Guernsey was two islands seperated by a small channel, which were connected at low tide, however at high tide they were completely separate (Guernsey has a 10m tidal range) during the 17th and 18th centuries, the French had a nasty habit of landing troops to try and take the channel islands, and when they did so on the larger island they were repelled by the local garrison, however when they landed on the smaller island if done at high tide then the British garrison had to march across a single connecting bridge to reach the invading forces or wait until low tide to cross elsewhere.

in 1803 they had had enough of this and decided to block off both ends of the Braye du Valle and then drain the interior, this began 3 years later, this meant that in the event of the french invading once more they could move troops far more easily.

Your islands

Yes bridges are expensive to build and maintain, however if other nations regularly attack then the ability to move troops without needing to wait for something else is important otherwise the invaders may fortify their position and make it a lot harder to take back. and anything your plot requires could cause a delay:

  • Tide
  • Availability of a ship
  • Adverse Weather
  • Even just the wind wasn't in the right direction to allow for a decent speed

All of these reasons played a part in real life naval combat at some point. so it makes sense that it would do so in your world to some extent as well.

After that its just justifying the cost and time. but quite often "we need to do it or someone will turn up and kill us" has been a fairly realistic excuse

  • Upvote just for "we need to do it or someone will turn up and kill us", the rest is icing – Dalila Oct 15 at 20:31

I'll go in a different direction, and I'll offer a picture instead.

To live there.

A big city-bridge

Maybe your people ran out of space in the mainland to both farm and live. Maybe the mainland is too volcanic, and a dangerous place to live. Maybe there is a monster there.

Maybe having a giant city-bridge just sounded too cool for the rulers to pass.

Still, the main gist of it is that the islands themselves wouldn't be the main living areas of your people, for reasons. Instead, they would live in gigantic bridge-cities - building the bridges not only would enable your people to travel but would also offer a better building spot than those dangerous/plagued/unstable/magical pony-infested lands.

Oh, also - if you have merfolks or other water based people, those cities could be an awesome place to live for them, too.

  • 1
    This has the Rule of Cool going for it, but as a practical matter, it would require a huge amount of material, and most of your reasons seem like they would rule out stealing material from the islands to build these structures. (Unless, of course, the OP's magic handwaving solves that problem somehow!) – ruakh Oct 16 at 0:07
  • @ruakh Indeed! My take on fantasy worlds is that once you add magic to it it seems a bit counterproductive to not use it for building even more awesome stuff! – T. Sar Oct 16 at 10:35

Basically the same reason Romans went into road building in a big way, efficient communication and movement.

Tonga tried to do this a long time ago. The reason was although you could move an army by canoe (they were big canoes), Land travel is much easier especially for large groups of warriors. Unfortunately for the Tongans it wasn't practical due to the deepness of the sea and distances involved. Nethertheless they did move some house size boulders in their attempt before their empire fell to bits.

Realistically their empire may have endured if they were able to move warriors efficiently and cost effectively. Without it they were always effectively outnumbered on any big island if there was a major insurrection with no way of communicating easily with Tonga let alone getting reinforcements.

Bridges are weather proof-ish, roads, well made roads, are less likely to experience massive loses of cargoes during hurricanes etc... As civilisation becomes more advanced, professionals more specialised, and processing more industrialised, supply certainty becomes more and more important, you not only have to deliver more materials to workshops and factories you have to deliver them more often and with fewer disruptions. Boats are more vulnerable to the vagaries of storm, wave, and accident than road traffic, and as such they are less and less desirable as a transport mode as civilisation gets more sophisticated. This is especially true when the technology of boat building doesn't advance into steel hulls and powered craft.

  • Well, weather proof is a stretch, especially over long distances with the tech level available. A decent pontoon bridge could be disassembled in storms and reconvened when required though, so you still keep a lot of the benefits. – Joe Bloggs Oct 15 at 10:51
  • 3
    @JoeBloggs The "tech level" is "a wizard did it", the OP specifically states that the bridges are built using magic. The description of the bridges is "titanic" which to me says huge, permanent, probably stone, spans. That's going to be a much more stable transportation net than wooden boats in stormy seas. – Ash Oct 15 at 11:19
  • Fair point. Missed the magic sentence. – Joe Bloggs Oct 15 at 12:02
  1. Because they can: to show off the prosperity of their empire or the vision of a ruler, etc.

  2. Because it is faster and easier to move a large amount of wares over dry land than over sea. You don't have to take into consideration the weather.

  3. How many people know how to navigate a boat over sea, even if it's just from island to island? Granted, people living on an island have a greater motivation to learn but if their work does not involve sea travel then they might not have the means to pay for the upkeep of a boat they rarely use. Also, learning to navigate the local atolls and currents probably takes years of practice.

Perhaps the ruler's family or caste never use ships. There could be a religious or social/traditional reason, or it could be the result of some events (feud against the shipbuilder caste, drowning of a past emperor, etc.). So far they've managed to build and maintain the empire through their armies and civil servants, but now there's a reason they must cross onto the other islands in person, so they need bridges.

Otherwise, it could be that one of the distant islands has a precious resource that cannot cross by ship. For instance, elephants that could be very useful as work animals but are afraid of deep water, or some precious substance that gets ruined when shaken by waves.

This is because local sea monsters started attacking ships. Those are smart and hungry beasts, and when a ship sank in a storm, they got a taste of its especially juicy cargo. They sank a ship or two, got what they wanted, and now they are raving for more.

There is the giant snake variety that undulates through the water and throws its head over the ship, down the other side and squeezes the ship (see Voyage of the Dawn Treader). There is also the burrowing fish that in just a few hours or so eats its way through the wooden hull (it usually burrows into coral reefs).

There is also the fact that forests are a limited resource on the islands; there are simply not enough trees to replace all the ships that were lost in the great storm of '36.

Not the answer you're looking for? Browse other questions tagged or ask your own question.