A Triarchal Menhir is a piece of Necron construct found floating around Szarekh's personal pimp throne, acting as bullet shields to protect the Silent King himself. They are probably called Triarchal Menhirs due to the possible fact that these two constructs may be controlled by the Silent King's duumvirate of Triarchs: Hapthatra and Mesophet. A Menhir is a man-made upright stone, typically dating from the European middle Bronze Age acting as their version of monoliths.
Despite looking like a giant floating wall, the Menhirs are actually armed with a weapon. These Annihilator Beams melts right through armour and hits like a freight train. Although they aren't that tough for a Necron construct, due to their nature as bullet shields, they would grow to become an extremely annoying Bitch to fight.
Triarchal Menhirs act as support vehicles for the Dais of Dominion. Because they always accompany the pimp throne, its movement speed is the same as the Dais as well as the same Toughness and Sv3+. However, due to acting more like a physical barrier, their WS remains shit at 6+ and they only have 5 Wounds and 1 Attack. Whilst this may not sound that impressive especially for a Construct, its weapon, the Annihilator Beam, is a giant FUCK OFF laser that can make superheavies feel the pain.
A Heavy 1 weapon with 36" range. The Annihilator Beam is an ungodly S12, AP-4 fuck stick that deals an automatic 6 Damage. Given the impressive BS of 2+ for the Menhirs, YOU WILL BE HITTING YOUR TARGETS EVERY SINGLE TIME. Moreover, there are two of these things, so you are dealing a flat 12 damage each round. This is without Szarekh pulling his own stunts mind you. So yeah, these things make Imperial Knights and Baneblades shit themselves. There is also the fact that they act as mobile shields, automatically giving the Dais an additional 10 more Wounds! Because fuck you that's why!