Aggressors Dev Diary #8 - Trade Routes

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Aggressors Dev Diary #8 - Trade Routes

Post by AlbertoC » Fri Aug 10, 2018 2:23 pm

One of the things which was pretty difficult to implement in Aggressors was the way the game handles resources.

Initially, the number and types of resources were hardcoded in the game's core and the only thing which could be changed (or modded) was the amount required for certain actions.

I didn’t like this approach. I knew that if there are mods focusing on different eras or genres, something like money or gold would not make sense anymore. And so I decided to define all resources externally in a modifiable file and connect them directly with unit actions that consume them, then the type of resource consumed and also the amount is entirely up to the externally-loaded rules.

Basically, every action in game, whatever you do, can cost you some resources. Building roads, bridges, settlements, irrigating lands, draining swamps, building improvements, healing... I could go on and on. It is entirely up to the rule creator (or modder) to set the resource costs for specific actions.
Aggressors: Ancient Rome itself comes with 10 different resources starting from gold, stone and coal through influence, knowledge and food to very special ones such as citizens and happiness.
Other mods might have a very different set of resources. For example: the Holland mod, the mod of one of our beta testers that we talked about few weeks ago, has two additional resources - cowhide and fish. Both are harvested in a different and very unique way.

But let’s focus on Aggressors: Ancient Rome only.

I already covered some of the special resources, their production and usage in previous dev diaries. I explained the use of Influence which is accumulated by cities and used on foreign towns to incite unrest. I also covered the citizens resource which is the main source of army recruits and the workforce and is therefore the backbone of the economy. Knowledge is another resource accumulated in cities, and is essential for research. But let’s not go into an exhaustive list of the resource types and instead talk about another aspect of the game – trade.


All the resources in-game are tradable. The only resource that cannot be exchanged is happiness. You can trade all mined or harvested resources as well as influence or citizens. And you can trade knowledge.
It sounds a bit artificial, but it is actually much closer to reality than it might seem on first sight.

I never liked the way technologies and inventions were traded in the Civilization series. The whole system of “I give you a Chariot technology and you give me Navigation" simply doesn’t make sense. Not only that such "technology-for-technology" deals are extremely rare even in modern history but I couldn’t find a single example in the ancient history. And I am not even talking about the fact that if you are good friends with a very civilized and technologically advanced nation, you could turn a barbarian tribe into a modern state in a few turns.

So, why do I think that the approach in Aggressors is better? Firstly, you don’t trade inventions but knowledge. You trade know-how of the scholars which can help you to understand the work of nature and progress faster to a new level of technological development.

Secondly, research of every technology requires a certain number of knowledge points. If you have excessive amounts of knowledge resource, you can even accelerate the time needed for research. The shorter the time, the higher the resource cost, of course.

Thirdly, even if there is a very generous player who is willing to give you a vast amount of "knowledge", you can accelerate the research process but you will not uncover technologies that are simply beyond your current stage of development. Minimum research time is set for every technology so you cannot just jump over several technologies in a turn. All this means that every player has to research every technology by his own means. The only exception is when you unite with another nation in a federation or you merge together. Then you naturally also get access to all the technologies of the partner player.

So, how does the actual trading work? It was really important for me to come up with such a system that would reflect the importance of trading for the life of all ancient nations.
As I said, you can trade all the resources except happiness. Trade exchanges are not one-off events but they lay foundations to long-lasting business relationships that can last for decades. No wonder that some negotiations can go on for several turns (years) as both parties need to set the right conditions.


How to start? You begin by establishing a trade route which is a path connecting your city with a city of the partner. Both partners need to have full visibility of one of partner’s cities meaning that they know where they are sending their merchants to.

The routes are calculated automatically so that the shortest and safest route is chosen. Depending on the length of the trade route, a so called "trade loss" is calculated which are basically overhead costs that will be deducted from the amount of traded goods.

Calculation of new trade routes is determined by many factors. It is not just the distance, but also the terrain types through which the traders will have to travel. If you build a dirt road between the trading cities (or at least connect some of the tiles of the trade route) you make the route safer and decrease the trade loss. Paved roads are even better, of course. If there are no roads, trading caravans usually use sea or river routes. It is indeed better to trade with a partner nearby with a good road connection (or secure sea paths) than with partner on the other side of the map. Sometimes the trade loss can go as high as 50% which you really need to consider before the trade is agreed upon.

With a trade route established, you decide what you want to sell and buy. You can either ask for a very specific deal or make a relatively open offer and give the partner room for negotiations. Another important point is that there is no "good" or "bad" deal. It is all about supply and demand.
The exchange starts when the deal is confirmed by both sides. And then the resources start flowing both ways every turn.

The trade routes might change over time, for example if an enemy blocks them. In such cases a new route is chosen (calculated) and when doing so the overhead costs might change as well, which could render the exchange unprofitable. As one of the trade conditions you can set a "trade stop loss" which defines what overhead costs you are willing to accept. If the trade loss exceeds this limit, the deal is automatically cancelled.

Of course, where there are resources (and money) involved, there are bandits and pirates who live off the loot they manage to get. There are two concepts of raiding in the game: independent raiders, who randomly attack the trading caravans and steal part of the traded goods; and state-controlled raiders, who take orders from their masters (other players) and their loot then goes to the resource deposits of their masters.

Bandits and pirates operate both on sea and land. All military units can turn into raiders when they are close to at least one active trade route. The more units you use as pirates and bandits, the higher the chance of success and larger loot. Of course, there is certain danger involved. Firstly if you use a unit for raiding, it is not fortified and has a reduced defense ability which makes it very vulnerable if attacked. Besides, raiding is perceived as a dirty practice and your diplomatic relations can deteriorate fast, not only with the victim, but with all other nations as well.

But you are free to choose your own path. After all, ancient history knows many examples of nations that survived solely by attacking traders and living off the loot.


Well, I hope I teased you enough to try all these aspects of the game yourself. Perhaps, pirates and thieves will rule the world under your command. Or maybe you will stand on the other side of the divide and be the one who frees the civilized world of all bandits on land and sea.

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