Tech level? Medieval.
Magic? Yep. More specifically: using levitation.
Forests surround my town, which is built in a wild forest on a river trade route to protect merchants.
How would I build my town to be spider proof?
The spiders are five feet tall and three feet wide, with web spinning abilities and poisonous venom.
For the sake of this question: please ignore any reasons a giant spider cannot scientifically exist.
Town of Orangey cinnamon peppermint. Ya no joke.
Spiders hunt in part by scent (apparently sweaty socks are a treat for them) and there are a few scents that repulse them pretty heavily, and as an added bonus...those scents actually smell decent to us. Surround the town walls with a ring of peppermint plants and wet down the walls with an orange cinnamon oil mixture. Peppermint oil works exceedingly well too.
The City of Nope
Due to an incredibly pressing need, the inhabitants have developed flamethrowers hundreds of years early. Children are given their first one as toddlers, and are trained and drilled in their use from an early age. The construction of the city is entirely stone, to negate the frequent use of cleansing fire.
Even fire isn't totally sufficient though, so once a year the residents do a water purge. The entire city is designed so that, through a series of gates and levies, the nearby river can flood the entire area. Basements have drains and sluices to handle the expected water flow. Everything perishable is picked up, families gather on their roofs (flamethrowers ready for surprise guests), and they party for two days as anything that did manage to survive is drowned or washed away.
They approached the fabled city surrounded by spiders, the boat rocking slightly on the massive river. Luckily, the river was wide enough where trees were not a worry, they only spanned a very short distance over the water.
One of the guards shot a spider skating quickly towards them, across the water. Spiders were not able to drop down from above but some were still a nuisance apparently.
As they approached the city, Tim saw impenetrable stone walls surrounding it. The city was dome-shaped, with a great amount of water falling down the sloped stone surface.
"But how do we get in?" he asked, and promptly fell off his seat as their boat started to rise up out of the river. His guide, rolling his eyes, continued the levitation spell until they were above the city, where there was a great rounded opening in the ceiling.
It appeared the water was supplied by the river, like some sort of fountain. The spiders were unable to climb the slick, wet stone with so much water flowing across it. Tim noticed a lack of trees above the domed city, probably kept cleared away for safety.
They entered the dome and Tim saw spikes below, with a few impaled spiders. "Some of them can jump" somebody explained, before Tim could could a word out of his opened mouth. They floated down, into an entry way and into the great city, where spider fur coats and web-spun armor were everywhere.
The Wasp Riders
The spider's natural enemy is the wasp. Wasps sting spiders and bring them, paralyzed, back to their nests to feed their young. That won't work on a fully grown giant spider (unless the town raises giant wasps, which I suppose is a possibility. They might make for a great air force, as well), but even if the wasps are small, they could sting the spider's young before they grew to be large.
Fire and axes would be the primary defense against them. One thing that would work well would be to find/train animals that fear the spiders, monkeys or loud birds. So when they spot a spider creeping about they will raise a cry to warn the watch. They will be armed with flaming arrows and axes should the spiders get close enough to need a more personal touch.
Of course the most important thing is to have the forest pushed back far enough to have good open land between the town walls and the nearest trees, allowing for a warning to be given in time. But that is good tactics for any town worried about attack.
I'm going to try using (abusing) the magic/levitation option.
The quiet town of Solar
The town is huddled in a circular fashion on both banks of the river. There are no walls, no fences, however the trees are cut and only grass grows for a good 50 meters between the forest and the city limits. The entire town is abnormally tidy and only a very few pets can be found.
The only sign of any danger lurking nearby is the often battered state of the merchants drifting along the river into town, and the town square. In the center of the square is an orb. A very peculiar one, for starters it floats, or levitates, hovering a few feet off the ground and never straying more than a few inches from its position. The orb is made of a strange material, liquid metal? light? maybe air or some unknown gas? Scholars have yet to decipher it. It was discovered by adventurers long ago. Every few seconds the Orb hums and sends a smaller identical orb swirling around in the air and eventually losing itself into the forest. This delights children who are constantly reminded by their elders not to follow them, for the forest holds many dangers; giant ugly disgusting evil nasty spiders. These spiders have no souls and desire only death and destruction. Killing them is considered holy. However nature (being a moron) has made them very tough to kill. In fact many wonder how the town manages to survive and thrive despite the 8-legged-monstrosities lurking at it's gates.
It was Gerald HairyNose who was born much too curious for his own good, that woke one day and followed a small orb into the woods. He walked for hours following the joyous ball of undetermined-material before an uneasy feeling crept over him. He thought he was going to die that day when the 10 feet tall spider caressed his spine with one of it's furry legs. But before it had a chance to enjoy Gerald's fleshy-ness fully, the little orb fused into the horrifying monster, immediately causing it to float, up up up and further away as the creature helplessly tried to grab branches and trees as it inched ever higher, over the canopy, and through the clouds, into the heavens and into the scorching sun where it burned and broiled and was incinerated past crispy cinder dust. Of course Gerald saw all of this, having incredibly amazing eyesight. He ran as fast as his hairy toed legs could carry him, back to the town where he sat in the tavern (which he's never left since) telling his story to who-ever would indulge him.
Cover your city with a net made of thick rope, (holes too small) for the big spiders to get in. Have patrols shoot any that climb on top with arrows, and kill any little ones that get through.
Or live in tunnels underground. But that's for dwarves.
Fight spiders with spiders. Raise jumping spiders as pets. Train them to hunt other spiders. (In Castle Roogna by Piers Anthony the hero gets a massive pet jumper spider.)
A corps of Spider hunters would make for a great faction in the city.
If the levitation spell is cheap or long-term and if it can be inverted to increase the gravity instead of decreasing it, you can surround the town with a ring of increased gravity, so that the spiders would break their legs if they try to go through it. (I hope that bigger spiders are more fragile than small ones.)
For citizen, there should be normal-gravity bridges over the ring, or levitating ferry, or whatever the city needs.
Just how big are the young when hatched? It seems to me that a small stowaway that hitched a ride in a merchant's wagon is a much bigger threat than the giant ones you can spot a mile away, especially if you can't distinguish it from a normal spider. And you'll need normal spiders, frogs etc., unless you want to be overrun by disease carrying insects.
Worst case: 2 stowaways form a mating pair and lay eggs before they are spotted
My suggestion, build it on an island in the middle of the river. Only allow people in overnight, not goods wagons. Any trade goods brought into town must be unpacked and inspected in daylight before being carried in by hand, especially firewood. Trading can be done in an outpost outside the town.
Logs for woodwork must be immersed in water overnight and turned over, in case there are spiders in a hollow. Ideally, you want your sawmill outside the town as well, possibly on a barge anchored 100m away.
Spider repellant, as suggested above, on the walls along with constant patrols will prevent any floating spiders entering your town. Boats/ bridges are a concern: try not to have a bridge, even though it limits your town's economy. Food should be grown on the island as far as possible, imports should be brought in by boat, that should not land anywhere that a spider can get aboard.
Selectively breed a species of silk weaving spiders to have a symbiotic relationship with the residents of your city, feed them milk/honey and let them catch rats and other spiders on their own. Their waste (drained rat/spider carcasses) can be ground up into fertiliser, unoccupied webbing can be harvested and spun, you can even milk their venom. This venom can be used for antidotes, injected in small amounts to build up resistance, used on arrows or mixed with alcohol for a special cultural drink.
Spun webbing and silk can be used to create strong rope, fantastic bowstrings, valuable cloth and biocompatible stitches. Heck, in a few centuries you could create a subspecies that creates clothing! It's not too far off their natural instincts: you get the spider to bite (you're either resistant or provided with the antidote) then stand still with your arms out and legs apart. The spider wraps you in silk and then you brush it off and feed it (or them) fermented/condensed milk as a reward.
Eventually they'll wrap anyone who enters their area of the hive and stands still long enough, just don't forget to feed them or next time they might be a bit more bitey. On the other hand if they're being fed like this on the regular, biting the person becomes an unnecessary step in the process and they might evolve to skip it.
I come from the land down under... ;)
