Do you mean physically or why it was possible?
Physically, he drew two intersecting circles with his swords, with the intersecting are being the gate to... Enoch Enterprises.
It was possible because apparently Archons had done the same thing with the swords before... it might be because the swords themselves are forged from stones that are at a leygate (Stonehenge) or it may be that the stone itself has some sort of magical properties, or the sword may have been imbued with the ability to create leygates while it was being forged (in the ancient language!
). Those are the reasons I got, anyway.