Battle Mechanics

Introduction: Before you know what ideally to attack with in Evony, you should have an idea of how the combat mechanics work. This will help you decide how many troops and of what type to send when you attack, and will help determine what type of defense you want to set up. Now some enemies have cookie cutter attacks such as a level 5 NPC can EASILY go down with 500 ballistae without taking any losses (assuming high level tech levels), but when you start looking at enemies such as a Level 10 or Level 12 NPC or above, then you have to look at what to send to minimize losses and maximize effectivity.
With this, you should hopefully be able to work out an attack (or know that you can't yet) no matter your hero size, army size, technology levels, etc...

Scouting

Scouting is the first and most important step to setting up a good attack. Without knowing what the enemy has, you will never be able to effectively setup a counter to what he has. By knowing what type of units and how many of each he has, as well as his tech levels (for most servers any good enemy will have level 10 tech levels by now, but not always the case) you can setup a solid counter.

Now to get a good scouting report, first of all you better have enough scouts to break through any defending scouts (only applicable in PvP, barbarian cities have no scouts and you can just send 1 scout if you like.) Also make sure to send a hero, preferably one with high intelligence rating to help improve your scouting. The third thing, is that the level of your Beacon Tower from the town which you scouting originates plays a factor in how well your scouting does. And the 4th and most important is your Informatics technology level (this is one of the cheapest and easiest techs to reach level 10 and should be done so early in your civilization.)

Combat Movement

Once you have a sizeable army built, it is time to start attacking. Keep in mind to always save enough army to defend against retaliation and ambushes. You don't want to go off to war and lose 95% of your army to win, just to have someone sneak in right behind you and grab what you worked so hard on.
The first step to understanding what to send is understanding how troops move, when they stop, who they attack, how much damage they do, how much they take, etc... Everyone should have a table of unit base characteristics as well as a table that includes modifications based upon technologies (all equations I use later are based on base stats and include tech level in the equation.) The key stats to know the modified value of your units are the Speed and Range (which are exactly what they sound like.) Speed is how fast your troops move across the field, and Range is how far beyond their current position they can attack. Below is a table that accounts for level 10 compass (100% boost to infantry speed) and level 10 Horseback Riding (HBR - 50% increase to mounted and mech speed)

The first unit to move in combat is the melee unit with the fastest modified speed. If both players have equally fast units, the defender moves first. The unit that moves, moves its complete distance or until bump, whichever comes first. i.e. 10,000 cavalry with level 10 HBR will move 1500 spots on the map or until it comes into contact with an enemy. Bump is when a unit runs into an enemy unit. Assume your cavalry are moving forward, but enemy warriors are only 1100 spots ahead of you, therefore your cavalry will only move 1100 spots and the warriors, when it is their turn to move, will not move at all since they are already at bump range. The exception to this movement rule is scouts and transports. They will not move forward and attack unless all other combat units are already dead, or were not preset to begin with.

Note: Ranged units are also an exception to this rule. Archers will move their 500 spaces (with compass 10) if they are not in attack range of any enemy units. If they are in attack range, they "stand and shoot." This means that as long as they can hit something without moving at all, they will hold their ground and shoot (see targeting under Combat Fighting section)

The standard starting field size is 200 units longer than the BASE range of the longest ranged unit on either side. Archers have 1200 base range so if they have the largest range on the field to start the battle, the field size will be 1400. The exception to this rule is if there are any Traps/Abatis/Defensive Trebuchets on the field, if so, the field size starts at 5200.

Note: Fighting does not occur until all units have moved, but where the units before them moves, can alter how far other units move.

Combat Fighting

After units move, they begin to attack each other. This is the second of 3 phases in each round. (1. Move 2. Attack 3. Remove Dead). The first unit to attack will be the fastest speed melee units on the field (tie still goes to defender.) Melee units will attack the first units they get to. If they run into multiple enemy types at the same location, they will attack the closest enemy, and the if multiple are at the same range, they will attack the enemy with the highest combined attack (Base Attack * Number of Units). This is why the rainbow can be so very effective (see Layering section.)

Ranged units (Archers, Ballistae, and Catapults) work differently. If AT's are in range, this will always be their target, regardless of how many there are. If no AT's are in range, they will attack the highest combined-attack ranged units from the enemy army that is in range. If no enemy ranged units are in range of your archers, but melee units are, the archers will shoot the fastest speed unit first.

Note: Remember that if Ranged are in range of ANYTHING, they will not move. Ranged will not move to get to higher priority targets, they will just shoot at the highest priority target that is already in range.

IMPORTANT: All units have the opportunity to fight. If enemy cavalry decimate all of your archers, all of your archers still get to take one last attack before being removed as dead fodder.

Enemy Fortified Range

This is a short section but VERY IMPORTANT. Enemies that you fight at their city will have increased range of approximately 4.5% per wall level, so with level 10 walls, enemies will gain a range bonus of 45% and this adds just like the archery range bonus. AT's have 2535 Range and Archers have 2340 Range while defending with level 10 walls and level 10 archery

NPC Respawn Rates and PvP Heal Rates

This section shows the importance of timing your wave well. Timing waves well can be easily achieved through Camp Time (last section of this guide). The respawn rate for NPC units in Evony is 1/3600 per second. Assume that the NPC had 100k warriors and you cleared them. If you come back in 45 seconds, you will find that there are now (45/3600)*100,000 warriors in the city (1,250 warriors). If you came back an hour later all 100,000 will have respawned. This is why you need to time your attacks well. On a scale of 100k warriors it is a non-issue but when you look at taking a level 12 NPC, there is 1,120,000 warrior, 162k swords, 100k cavalry, etc... and they will all respawn at this rate. This becomes an even larger issue when taking a 14 and above.

Note: If the enemy has 200k cavalry and you only kill 125k of them, the respawn rate is still base upon the 200k cavalry number, not off the 125k that you killed. So if you came back 1 minute later with your next attack wave, you will find the 75k remaining cavalry that you didn't kill plus (60/3600)*200,000 cavalry in the town. The respawn will continue until they unit reaches its original number.

In PvP attacks, there is no respawn time. Players get heal rates instead, and in PvP this is inversely based upon your honor. The more honor you have, the lower your heal rate is. The heal rate varies anywhere between 10% and 50% healable casualties.

Layering (Rainbow)

Hopefully after reading the combat movement section, it started making you think of layering. The thought that "if I send 1k pikeman, can they occupy a 100k cavalry for a round", delaying him from reaching your 99k archers you sent with him, essentially giving them an entire extra round of shooting. This one round of shooting can inflict around 60,000 cavalry kills with a 200 Attack, 100 Leadership hero. Without a single pikeman making the cavalry stop for one more turn before reaching your archers, the 100k cavalry would reach your 99k archers reducing the archers damage to 15,400 cavalry kills (see range effects on archer in Attack equation section) and the cavalry inflicting enough damage to kill 196,000 archers (a complete loss.) Layering 98k archers with 1k swordsman and 1k pikeman vs. the same 100,000 cavalry will buy your archers 2 free shots, because one unit type can only attack one unit type per round (i.e. cavalry can attack pikes or swords in one round, but not both.) Below are examples of no layers, bad layering, good layering, and the occasional need to send a bomb wave (this will reduce an enemy unit enough to kill it in less rounds, improving your movements relative to enemy movements)

Note: There are 2 reasons you do not want to send just 1 unit layers instead of the 1-2k that are generally done: First is enemy Traps/Abatis/DTs will generally kill that single unit before he layers anything. Secondly is Spread Damage. Spread Damage is the idea that if one unit type killing another is SO overkill, that it will actually hit 2 unit types in a single round. The exact amount of overkill is unknown for sure still, but the generally accepted rule is 100x overkill, expect spread damage.

 

Attack Equation and Derivation

Can be found in Birtle's post titled "Combat Calculator."

Traps and Wall defenses and Suicide Waves
Wall defenses all follow different rules.

Archer Towers - They cannot move, and they are the first units targeted when other range can reach them. They do decent damage and are the only wall defense that can attack more than one time without being rebuilt or repaired through techs. These should primarily be used in a compact defense (no 5k range wall defenses present)

Defensive Trebuchets and Logs seems to be fairly useless wall defenses to me. I keep 500 defensive trebs on my walls as an additional range setter, but I doubt they actually do any good

Traps and Abatis are unpredictable wall defenses but some of the best out there. They take up the least wall spaces an offer many kills as well as expanding the field size to 5200 spaces. They also do decent damage. I generally fill my walls with decent amounts of these and only these in my 5200 range towns.

Suicide waves are used to destroy enemy traps or weaken enemy units. The generally accepted suicide wave will be 1k warriors + 1k cavalry (to clear traps/abatis) and will be sent with garbage heroes.