Zverák is large, make no mistake. Originally, Slayers and Scouts had to travel entirely on foot, and this became problematic, as missions to far away and hard to reach lands became more difficult and casualty-prone. The mages of The Citadel decided that the best solution was to use highly advanced teleportation magic, and create gates from one area to another.
This manifested in the Portal Stones. Erected to look like regular rocks, they are unnoticeable to everyone outside of our order. However, on their faces is the symbol of The Citadel. They are not usable at first, but if one has placed his blood in The Citadel’s fountain, and then in the Portal Stone’s symbol, he will be able to move between the two. With this ingenious system, to be able to infiltrate The Citadel through the Portal Stones, any invader would have already had to have infiltrated naturally.
Portal Stones are rare, and are place only to prevent the most hazardous journeys. Currently, portal stones are in the northern tundra, the southern forest, and the marsh island of Zanar, even further south.