I need a fortress that will stand up to the following magical creatures, must be above ground and have a fairly large (20-50 thousand) civilian population as well as a roughly equal number of soldiers, middle-ages level technology:
Dragons: Enormous (75-100 ft. long) flying creature, arrow proof (although a quarrel at fairly close range will pierce them) scales everywhere but wings, breaths fire, low (cow-like) intelligence.
Drakons: Much smaller, (10-12 ft. long) flying creatures, similar scales to dragon, cannot breathe fire, pack hunters (groups of 10-20) , medium (dolphin-like) intelligence.
Orthrus: Two headed, 4 ft. tall wolf, thick steel fur that can deflect slashing attacks, pack hunters (20-30) , medium (dolphin-like) intelligence.
Diatrima: Enormous carnivorous birds (8-10 ft. tall), axe-like beak, live in groups of 3-4, low (cow-like) intelligence
Feralt: Humanoids with various animal features (eg. ram's horns, wolf fangs and muzzle, feathers, claws), live in tribes of 500-1000, but will band together in large, 10-15 tribe alliances to attack the city, use Diatrima and Drakons as mounts, use Orthrus as hunting/war dogs, high (slightly sub-human) intelligence.
Spinterra: 20 ft. long porcupine with venom-coated steel spines that they can launch up to 75 ft. Can burrow (fairly quickly) through most substances including rock. Low-Medium (Lion-like) intelligence.
Squirreloid: 5-6 ft. tall bipedal squirrel with extremely sharp teeth and claws. Very High (human) intelligence. Can climb most surfaces easily, but fairly rare. Do not work together with Feralts. Live in teams of 10-20.
The biggest goal of all these creatures is to kill as many humans as possible, low intelligence creatures merely attack all humans they see, Feralt make complex military alliances and attack plans.
Humans (but not creatures) have access to magic with the following laws:
- All magic requires runes and a verbal activation (saying 'magic words' that correspond to the runes)
- Any spell lasts a maximum of one minute (no enchanting)
- Any spell has a certain maximum amount of power, and will not complete tasks over that power (you can create a small fireball, but can't make a storm or teleport)
- Any spell takes three seconds to take effect after the verbal component has been said (gives time for a counter-spell)
- Runes can be traced on a surface (temporary rune) and can then be activated only by the maker, or engraved/written (permanent rune) where they can be triggered by anyone holding the object.
- All enemy creatures carry a radius (roughly their own length/height on each side of them) where magic cannot affect anything (but you can do things like throw a rock with magic into the radius, it just stops being propelled by the magic, but keeps its momentum)
I would also like to know if you find any loopholes using this magic system allowing things like teleportation or mind-control, anything I probably wouldn't like.