Relics are a special item that can be traded on the market or used to increase a specific trade skill. You can find them through random global drops, tournaments, scouting or through using a key.
Relics can be invested into specific tradeskills by going into the action menu for that specific trade skill. The cost per single unit goes up by 1 relic for every unit purchased. Bulk purchases cost the same as buying them on a 1 by 1 basis.
You can invest them as follows:
Increases experience for every action performed while using this tradeskill by 0.2 per investment. Best to invest to X.6 due to rounding as of right now.
Increases T1 resources gained by 0.015 per investment. This boost is lightly better than workforce or levels, but it doesn't really pay off until you have invested quite a bit into it. Also has diminishing returns at higher tiers.
The simplest relic investment, adds +3 to you workload per investment. More idle time, if that's what you like.
Drop +: Edit
Adds (multiplicative) 0.5% to the global drop rate per investment. For instance, if you had 100% drop+, (which costs 20,100 relics to invest to that level), and the global drop rate was 1/3000, it would now be 2/3000.
Res. Luck: Edit
Adds a % chance to each tier to find resources of each tier per investment, with diminishing returns at higher tiers. For instance, +6% Res luck gives T1 6%, T2 4%, T3 2.7%, T4 1.8% and T5 1.2%. This stacks with any kingdom bonus.