Please look at NPC safe ballista levels and NPC trans levels for a visual explanation of components found in this post.
Probably the most frequently asked Evony question is “What techs do I need to farm NPCs using ballistae so that I don’t lose any?” The most important techs are Archery and Horseback Research (HBR). Other techs, such as Military Tradition (MT), Iron Working (IW), Medicine (MD), and your hero attack and int-skills, will affect the number of ballistae you need to do it without losses. But without the right combination of Archery and HBR, you will take losses regardless.
There’s a lot of mostly correct, but sometimes inaccurate information out there. THERE IS NO FORMULA. (Or rather it’s too complicated to be useful.) There is, however, a very small table to help you out.
NPC 4′s
Arch 6: HBR 6 or 10 (only)
Arch 7: HBR 1 and higher (Any except HBR 0!)
Arch 8: AnyArch 9: AnyArch 10: Any
So here’s a simple rule:
HBR 5 and Arch level 7 and above will work.
HBR 6 and any Arch level (6 is required to build ballistae) will work.
NPC 5′s
The requirements here get much narrower:
Arch 8: HBR 5 or 6 (only)
Arch 9: HBR 3, 8, 9, or 10
Arch 10: HBR any
So one general method is to obtain HBR 6 before farming anything and to start with NPC 4′s. When your archery reaches 8, start on NPC 5′s. Then before your research for Archery 9 completes, quickly get through HBR 7 and all the way up to 8, ideally finishing HBR 8 and Archery 9 simultaneously (in two different cities). You can then farm NPC5′s again.
Tip: Start Archery 9 in a different city than where your level 6 stable resides. This way you can do the research on HBR at the same time (and preferably, just before) Archery 9 completes. Remember that you cannot farm 5′s with Archery 9, HBR 6/7 without taking heavy losses.
Why?
Some people like to know why this is so strange. I’ll briefly summarize the main two problems.
Problem 1: Your ballistae don’t stop early. Your ballistae, like other mechanics, move at their base speed multiplied by HBR (1 + 5% per level). (The idea is, the ballistae are being pulled by horses.) Ballistae, just like every other mobile ranged unit in the game, will either not move at all (if something is in its firing range) or it will move full speed ahead. They will not stop half-way just because that would put them in range of, say, the ATs, even if moving further would put them in the AT’s range. Yes, your archery units are stupid!
NPC 4′s technologies and walls are all at level 4, while NPC 5′s techs and walls are at level 5. As the wall level and archery level increase, so does the range of the NPC’s Archery Towers (ATs), enabling them to shoot further onto the battlefield. So between the two NPC levels, your ballistae need to stop a different distance away in order to not get hit.
Problem 2: The faster the ballistae move, the fewer shots they get off. It makes sense, doesn’t it? The two armies are charging at each other — even the defending archers charge. In some scenarios, your ballistae don’t kill enough of the front wave to be able to kill off units in the back wave before those units can reach and damage the ballistae. In other scenarios, your ballistae and the defending archers hit each other simultaneously, even though the ballistae normally out-range the archers. These problems present themselves also when you use two few ballistae for a given MT/Attack level (and on rare occasion, when your IW/MD/Int are too low). If you see battles in which 3 or 4 ballistae are lost, it was probably one of these back line units that managed to scratch a few of your units. If it’s 50 or 60, it was probably the archers-ballistae collision.
For some of these combos, you can use a number of archers — 1000 is usually safe — to mitigate these effects. This tactic can be sometimes used with an otherwise bad HBR/Arch combo. But it’s only when the cause of ballistae death is Problem #2, not #1 above, where the warriors will help.
So, that’s it in a nutshell. Happy farming!
