This pack, one of six included in the Civilization VI: New Frontier Pass, introduces Basil II as the leader of Byzantium and Ambiorix as the leader of Gaul. The Byzantine Empire can subjugate enemies with religious and military might, supported by their two unique units: the Dromon ship and the Tagma Heavy Cavalry unit. The Gallic horde focuses on military flexibility boosted by a backbone of culture and production with their unique Oppidum district.

The Byzantium & Gaul Pack also adds the Dramatic Ages game mode, the Highlands Map Type, and two new World Wonders. More details below:

Byzantium

• Unique Civ Ability: The "Taxis" ability gives units additional Combat Strength or Religious Strength for each Holy City converted to Byzantium's Religion. Byzantium's Religion spreads when an enemy unit is defeated. Cities with Holy Sites earn bonus Great Prophet points. 
• Unique Leader Ability: Basil’s "Porphyrogénnētos" ability allows Heavy and Light Cavalry units to do full damage against cities that are following the same religion as Byzantium. Basil gains the unique Tagma Heavy Cavalry unit when the Divine Right civic is discovered.
• Unique Unit: Byzantium features two unique units: The Dromon ship replaces the Quadrireme, has greater range, and receives additional Combat Strength against enemy units. The Tagma replaces the Knight, and grants nearby land units additional Combat Strength or Religious Strength.
• Unique District: The Hippodrome replaces the Entertainment Complex district, is cheaper to build, and provides additional Amenities. A Heavy Cavalry unit is also granted when the Hippodrome and its buildings are constructed.

Gaul

• Unique Civ Ability: The "Hallstatt Culture" ability triggers a Culture Bomb when Mines are built, and allows Mines to provide a minor adjacency bonus for all districts. Specialty districts cannot be built next to the City Center and do not receive adjacency from other districts.
• Unique Leader Ability: With the "King of the Eburones" ability, Ambiorix’s civilization gains additional Culture based on unit cost when a non-civilian is trained. Melee, anti-cavalry, and ranged units receive bonus Combat Strength for every adjacent combat unit.
• Unique Unit: The Gaesatae replaces the Warrior. It is more expensive to train, but receives additional Combat Strength when fighting stronger units and district defenses.
• Unique District: The Oppidum is cheaper and available earlier than the Industrial Zone, and unlocks the Apprenticeship technology when constructed. It is defensible, offering its own ranged attack, and receives a major adjacency bonus from Quarries and strategic resources.

Dramatic Ages Game Mode*

In this optional, specialized game mode, civilizations always enter a Dark Age or Golden Age in every new era, both of which are more potent than ever. Dramatic Ages mode also includes these exclusive rule changes:

• New Policies: Players gain access to special Social Policies instead of making Dedications, including new and updated Golden Policies and Dark Policies that offer more flexibility and power.
• New Golden Age Boosts: Entering a Golden Age with extra Era Score will increase citizens’ Loyalty pressure on nearby civilizations.
• New Dark Age Challenges: The chaos of Dark Ages can cause cities to rebel!
• New Era Scores: Players gain Era Score by completing Technologies or Civics and promoting units through combat, as well as from Historic Moments.

*Requires the Rise and Fall or Gathering Storm expansion to play.

Additional New Content

• Biosphere World Wonder: Increases Appeal from all Marsh and Rainforest tiles. In the Gathering Storm expansion, it boosts Power and Tourism. In other rulesets, it grants bonus Science for every Marsh, Rainforest, or Woods in the city that built it.
• Statue of Zeus World Wonder: Gives free military units to the city that controls it and increases Production towards anti-cavalry units.
• Highlands Map Type: Play on maps dominated by hills and mountain ranges.