The setting is a generally nondescript mid-medieval vaguely European society. No magic is present, except what is explicitly discussed in this question.

Twenty kingdoms, connected by trade routes but distant enough to have mostly segregated politics, are functioning as normal one day. The next, a giant tower explodes through the ground in the dead center each of their largest cities, killing civilians and destroying buildings.

The towers are met with (obvious) concern, but eventually several kingdoms discover that each tower has a doorway (wide and tall enough that two trade wagons abreast can comfortably, and easily pass through), and in fact each tower has exactly one doorway, with no other openings whatsoever. Some brave (or foolish) explorers determined that, by magic, through a series of large empty rooms these doorways connect with the other kingdoms' towers.

The towers appear to be perfectly indestructible. If the doors are barred from the outside they are impossible to open from the inside (although just like normal doors or gates, they cannot be instantly closed). There is nothing to be found in the towers' rooms, just empty slate floors, marble walls and ceilings, and great openings interconnecting them.

Traveling from one doorway to another is a matter of hours, instead of the weeks or months of travel required to travel between the kingdoms previously.

They've just discovered a means to drastically, drastically reduce the time to move trade, people, and potentially armies.

Assume most of the kingdoms aren't stopped by superstition.

Specifically dealing with trade and defense against invasion, what would an intelligent, sensible policy for a kingdom to adopt in this situation? What is the best policy to balance the advantage of trade with defense of the kingdom with this new opening (effectively forcing twenty of the largest cities under different kings to share borders)?


For defense, the area around the new tower will be cleared of all existing buildings. A double spiral path winds outward for several loops around the building. For normal usage, one spiral will be used for outbound traffic and the other will be for inbound. These roads are wide enough for wagons to be pulled through the curves, possibly wide enough for wagons to pass one another should one break an axle or something.

These roads are separated by thick stone walls. The walls are tall enough prevent climbing. The walls are wide enough to allow defensive works to overhang the pathways with murder-holes and bridges allow quick movement to any point on top of the spirals. Towers on the outside of the spirals contain the only stairways to the top.

Some of the bridges also house the winches for a portcullis below them, allowing the spiral pathways to be closed off against any invaders.

The area within the tower may be an absolute nightmare of logistics managing traffic to and from 20 separate endpoints. Unless each tower has a unique, non-overlapping, 2-lane path to each other tower, traffic will constantly be running into each other.

The kingdoms may actually come to an agreement where traffic from one kingdom is limited to only a few destinations and then only on a set schedule. The destinations would be set up so that you could still reach any other city, you may have to pass through 1 or 2 other cities first though.


Start the United Nations!

Assuming these towers are basically wrappers to some extradimensional space-time where people can meet in passing and otherwise interact with each other, each nation should send a small contingent of representatives to camp out inside the tower. These contingents can negotiate to control the flow of goods through the newfound portals and, in times of need, quickly pass word to seal the doors to their respective nations. In general, however, the Towerspace is agreed to be neutral territory and the presence of an excessive military force is deemed a violation of the Tower Treaty requiring corrective action from the remaining nations.

The empty rooms are quickly populated first by diplomats and soldiers, then by merchants, and finally by the commoners/travelers. In the end, you end up with the World City, a glorious mashup of every nation with access to the Towerspace.

Of course, creating articles to allow another nation to join would be hard...

  • $\begingroup$ Assuming that all 20 nations decide not to have a war $\endgroup$ – sdrawkcabdear Nov 15 '16 at 18:46

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