A portal is a magical gateway between locations. Portals can only appear at auspicious moments. Some of these are described as being high noon, sunrise, a god's birthday, an alignment and various other things. Most magicians memorize these moments, but Sadie Kane believes that these auspicious moments are happening all of the time and thus a portal can be opened nearly any time of the day. Objects that are naturally inclined to be gateways are obelisks, pyramids, and items with significance in Ancient Egypt, such as the Temple of Dendur. Once a portal is opened, they require a twelve-hour cooldown before either the portal of origin or destination can be used again. Objects that can be used don't have to be from Ancient Egypt itself as long as they are representative of it: Bes is able to use griffin statues in London to open a portal that were build well after Egypt fell and later the Egyptian Bridge in St. Petersburg which was built in the 18th century. Where the portal comes out depends on where the object it connects to is in that city. For example, for London there are many possible objects and unless one is specified, its apparently random, but in Alexandria the portal is underwater as the object is also there. If a portal is opened with only a country in mind its not specific enough, the location that it goes is the default portal for that country. For example, Sadie Kane opened a portal with the destination of America in mind and it sent her to the Washington Monument, the default portal for America.
Portals cannot be used during the Demon Days starting at sunset on the 26th, but it is possible for a god of magic to open one or a godling who has fully merged with their god. Gods can open portals, but most have the same limitations as magicians, needing powerful enough artifacts to open one between. However, both Thoth and Isis can open portals anywhere as could Sadie Kane while merged with Isis and Anubis has shown this ability as well. Bast lacked the ability to open a portal while Bes was skilled at it and seemed to have a great knowledge of portals and their locations. Ptah could only open portals like a magician, but he could open one in an area cursed to prevent that and he could use a god as the anchor on the other end. While magicians can only open portals at auspicious moments, gods seem to be able to open portals at any time as Bes never seemed to consult any sort of timetable when transporting Sadie and Carter around.