The Realm Guardians

Throughout the world exist magical columns that have a single dragon statue perched upon them. While the column is often made of rough stone the dragon is always crafted of precious metals and gem stones. These dragons come in every color and style that actual dragons do. Would be theives have learned that there are severe consequences to distrubing the statues and the lucky ones live long enough to tell others of their misfortune.
Such individuals feel stalked and catch glimpses of a dragon like shadow following them. This is all a prelude to them suddenly being plucked from the ground and devoured by some invisible creature. Regardless how damaged the statue was by the theives actions it is always found in perfect condition after whatever the theif took is recovered.
While no one knows who constructed these towers but over time powerful individuals have started to piece together what they do.

Anti-Realm Coin Aura

One of their functions has become obvious to travellers carrying realm coins. These statues form lines that seem to strech on forever, spaced a few miles a part from each other at regular intervals. Anyone passing between these statues does not seem to suffer any ill effects, but the same can not be said for any money they are carrying. All realm coins carried by the individual become non-magical and transform into blank disks of lead.
For this reason, merchants that travel beyond such borders must convert all of their money into precious gems and/or trade goods before setting out. It also makes trade beyond such borders difficult, since bread coins (while unaffected by the statues) are typically not accepted in distant lands.

Anti-Magic

Another effect that powerful wizards have discovered is that the realm guardians seem to prevent certain kinds of magic from working across it's borders. Those discoveries are as follows:

• Spells that allow communciation like sending simply fail to function. This includes even very short range magic like message and magic produced from items like sending stones. These spells function perfectly fine if both the sender and reciptient are on the same side of a realm guardian.
• Teleportation magic also does not function across it's borders even infallible magic like Teleportation circle does not work. Thankfully the caster isn't sent off course the spell simply fails to work
• Most forms of planar travel do not function inside of an area encircled by the realm guardians. The exception to this is travel to and from the fey wild. It's not known if the fey made a deal with those who constructed the realm guardians or if its due to some other reason. Anyone attempting to travel to a barred plane has reported that it was like slamming into a wall of force at considerable speed

Anti-Invader

Most creatures born or created outside of an area encircled by realm guardians find that they can not physically pass between them. However, it doesn't prevent all travel of such creatures. If the creature's alignment is within one step of the alignment of the dragon depicted, and they carry no ill intent, they are generally allowed to pass it's borders. Those born or created within the borders of an area encircled by realm guardians seem to be able to freely leave and enter the area regardless of intent. Though there are tales of those who were exiled being unable to re-enter after they left the area encircled by the realm guardians.