Archway/1.03.24

Empire
The Archway serves multiple purposes for the Empire and make it a rather important building. Firstly, its very presence allows for the production of Halberdiers. This ensures that the building needs to be on the field at all times. If destroyed, you would want to re-build it. Secondly, the Morale skills it researches offer a permanent boost to your troops attack speed, as well as a slight boost to your army limit / population cap. Although minor improvements, they're improvements nonetheless. And finally, the Fame skills it also researches make producing Mercenaries viable by reducing their cost, and even by up to 50% once you have all three of the researches.

The building is small and even quite durable for its size, allowing it to weather minor enemy assaults and can be placed easily within your base, slotting it in those tight spaces which would otherwise be wasted building room. But its cost is a little higher than usual and the Fame skills take a very long time to research, not to mention they come with a hefty cost. Ideally you would want to focus on the Morale skills first because of this.