Videssos cycle
Harry Turtledove
 During an encounter with a Celtic force, a Roman legion is magically transported to another world when the two opposing leader’s swords touch. The Roman force and Celtic leader find themselves in an empire called Videssos. This empire hires them as a mercenary force to help defend their lands from an enemy nation, Yezd. It quickly becomes apparent to the leader of the legionaries, Marcus Aemilius Scaurus, that the Empire is rife with political intrigue. With steadfast loyalty to the Emperor and a certain bull-headedness, Marcus manages to safely navigate the particularly dangerous political landscape and advance the place of himself and his men. At a party to celebrate the arrival of the Romans held by the Emperor Mavrikios, Marcus, slightly inebriated, slips on the floor and bumps into the emissary of Yezd, Avshar. He tries to apologize, but is rebuffed and a duel results. Marcus wins, but chooses to spare Avshar rather than kill a helpless man. Avshar then sends an assassin after Marcus, but the assassin fails and the Emperor uses this attack as an excuse to declare war upon Yezd. Avshar leads the enemy army of Yezd nomad warriors against Mavrikios' Videssos soldiers and mercenary forces. When Avshar casts a magic spell at the commander of the left wing, Ortaias Sphrantzes, the entire wing of the army is set into chaos as Ortaias turns his horse and flees at full speed. Only the quick actions of Gaius Philippus, the sub-commander of the legion and the aid of a clever ally Laon Pakhymer kept them from falling to the nomad forces. Mavrikios, seeing his grand army destroyed, led a charge of his personal bodyguards directly at Avshar, hoping that he could at least take the life of this one great enemy. He fails and is struck down. His brother Thorisin, leader of the right wing of the army is forced to flee and Yezd has won the battle. Both Ortaias and Thorisin declare they are emperor of Videssos after the battle, but Ortaias, with the help of his Uncle, controls Videssos the City. Civil war erupts. Eventually, Thorisin emerges victorious as the citizens inside Videssos the City turn on Ortaias and open the gates for Thorisin's troops. It is revealed that the leader of the city guards put in place by Ortaias was none other than Avshar in disguise. Avshar manages to escape the city. In an attempt to bolster his forces, Thorisin sends emissaries of his own to other countries to recruit more mercenaries for his Empire. Unfortunately, before he can organize any such force, a group of his own mercenaries turn on him and declare the western half of the empire their own. Thorisin sends a force, including the Legionaries, to the west to put down the rebelling mercenaries while he dealt with threats to the east. Half the western army turns in favor of the usurping forces and Marcus is forced to take over and do the best that he can to follow Thorisin's orders. He engages in guerrilla tactics that eventually bring down the mercenary usurpers. As he is bringing the leaders of the rebellion back to Thorisin in Videssos the City, he is betrayed by his wife who frees her brother and the rest of the prisoners. He returns to Videssos in shame. While suffering through the betrayal of his wife, Marcus begins a relationship with Alypia, the Emperor Thorisins niece. When discovered, he is hauled to jail to await his fate. Thorisin sentences him to death, but commutes the sentence provided that Marcus, alone, remove from power a heretic to the west. Marcus agrees on the condition that he can openly suit Alypia. Thorisin agrees and sets Marcus on a boat to his destination. After successfully defeating the heretic, Marcus flees the city in front of an advancing barbarian army (his own Legion coming to rescue him.) He signs up with a caravan train and ends up going to Mashiz, capitol of Yezd. There he witnesses the overthrow of the King of Yezd by Avshar. Fleeing Avshar, Marcus manages to escape in the company of an army of Nomads who have come to seek revenge upon the Yezd. Together they flee to the east to find Thorisin and plan a campaign against Avshar and the Yezd. At the final battle, Avshar kills the Videssian Patriarch and seems on the edge of total victory when Marcus and Viridovix touch their blades to one another again and the released magic transports Avshar to another world, apparently Skotos' hell. These acts lead to Marcus being granted title and significant position in the empire and his marriage to Alypia.