Gordius Wheel

Strictly speaking, the Noble Phantasm is the Gordius Wheel (ゴルディアス・ホイール), Wheel of Heaven's Authority (神威の車輪); just like what Enuma Elish is to Ea, Via Expugnatio (遥かなる蹂躙制覇) is the trampling attack performed with the Gordius Wheel.

The damage is decided by two rolls, for the hooves of the divine bulls and the wheels of the chariot. Along with all physical damage, there also is the effects of lightnings, the manifestation of Zeus. Should the target fail its STR check, additional damage will be dealt.

Source: status page of Fate/Zero #3.

The Gordius Wheel
The Gordius Wheel is a war chariot led by two divine bulls. Both the bulls and the wheels of the chariot can create lightning strikes when hitting the ground - or even the air, as a manifestation of Zeus. Each of these lightning strikes generates an amount of prana that is equal to a full force strike from Saber or Lancer.

The bulls were originally an offering to Zeus from the king Gordius, but Alexander claimed it by cutting the knot with his sword. It apparently is what granted him the Rider class. The Noble Phantasm is summoned by cutting through the air with the chypriot sword, just like the legend; the chariot comes out of the torn space.

Waver Velvet compares its power to that of a strategic bomber, guessing it could turn Shinto into scorched earth in under one hour. That is because the chariot is far more robust, and the bulls are, according to Rider, Zeus's offsprings.