The two distinct advantages offered by portal axles are the increased ground clearance and that they allow the vehicle to drive at the same power with reduced torque. The portal axle is sometimes referred to as a drop-gear configuration, as well.
The portal axle allows for increased ground clearance because the axle tube and differential casing are higher under the vehicle than a normal axle. The differential casing is a specific type of planetary gear train. The gearing that is inside of the portal housing is what transfers the power from the axle to the wheels. A normal axle is a part of the frame or chassis of the vehicle. To increase the ground clearance of the vehicle even further, the differential casing can be reduced in size.
The gear reduction at the wheel is what allows the torque to be decreased on all the other drivetrain parts. This is due to the way the gearing ration sits inside the portal drop box. The full torque only happens at the wheels because of this.
Some off-road vehicles with portal axles include the Volkswagen Type 82 Kubelwagen, Volkswagen Type 166 Schwimmwagen, Mercedes-Benz Unimog and the Toyota Mega Cruiser civilian model. Portal axles can be purchased and placed in many off-road vehicles as well.