The fighting force drawn from the enslaved Remans of the dilithium mines, used by the Romulans as expendable troops in the Dominion War and led by Shinzon in his coup of 2379.
The Remans are the subject caste of the Romulan Star Empire, confined to the dark side of Remus and worked in its dilithium mines. Star Trek Nemesis explains that the Romulans threw them into the worst fighting of the Dominion War as assault troops, where the human clone Shinzon rose to command them and won a string of victories.
With that reputation and the support of disaffected Romulan officers, Shinzon has the Senate murdered with thalaron radiation and installs himself as praetor. His Reman soldiers, led by his telepathic Viceroy, crew the heavily armed warbird Scimitar.
They board the Enterprise-E during the battle in the Bassen Rift and are beaten back by Riker and Worf, and the Viceroy falls to his death. The remaining force dies with Shinzon when Data destroys the Scimitar.