Portals reduce march time to a selected location, acting like a shortcut to your city. To open a portal, click any location on the world map and select the “Open Portal” option. You cannot open portals on the territory of any clan other than your own. You also cannot open portals to other kingdoms outside the Clash of Kingdoms. You must build the Portal Master to place portals on the map.
Whenever you start a march, the distance between its destination and your city is calculated dynamically. The march always starts from the closest point to the destination and returns to the nearest point. Since portals act like open gateways to your city, if a portal is closer to the destination than your city, then any march to that destination will start from that portal. It will also return to that portal, given it's still open.
The player who opened a portal can close it anytime, even if allied armies are marching back to it. In this case, the marches will be redirected either to the next-closest portal available or directly to players’ cities, depending on the distance between the marches’ current location and players’ cities.
Similarly, if you teleport your city closer to the march destination than the portal the march started from, your troops will return directly to your city.
If you place a portal at the destination of an enemy march, that march will engage the portal once it reaches it.