Altars



Demon Altars and Crimson Altars are naturally-occurring crafting stations found mainly in and around Chasms in The Corruption or The Crimson, and less frequently underground. They are used to craft boss-summoning items and the Night's Edge. Altars emit some light, making them easy to spot. They cannot be freed, picked up, placed, or crafted.

After a world enters Hardmode, they can be destroyed with Hardmode-tier hammers, but attempting to hit them with a hammer before Hardmode or a hammer with less than 80% hammer power causes the player to lose half their health, while leaving the Altar unaffected.

Hardmode
After the Wall of Flesh has been defeated in a world, Altars can be destroyed with the Pwnhammer or any superior hammer. If a player attempts to destroy the Altar with a lesser hammer, or in a world in which the Wall of Flesh is not yet defeated, the Altar will be unaffected and the player will lose half their current health, as stated above. Each destroyed Altar will spawn a Wraith and causes one type of Hardmode ore to appear in the world, with the appropriate message displaying in the player's chat: "Your world has been blessed with (ore)!"


 * 1) First Altar: Cobalt Ore or Palladium Ore, chosen randomly.
 * 2) Second Altar: Mythril Ore or Orichalcum Ore, chosen randomly.
 * 3) Third Altar: Adamantite Ore or Titanium Ore, chosen randomly.

Players will be able to find these new ores scattered across the Underground layer to near-Underworld levels, with them replacing most blocks created during world generation. They will spawn at random locations in varying quantity, in places explored and unexplored alike.
 * Which ores are generated is not determined until an Altar is smashed. For example, it is not determined if the world has Cobalt or Palladium until the first Altar has been smashed. The same goes for Mythril/Orichalcum with the second Altar, and Adamantite/Titanium for the third.
 * Subsequent Altars destroyed will begin the cycle again, though the fourth to sixth Altars will drop half as much ore as the first ones, the seventh to ninth will drop only one third of the ore of the first ones, and so forth. This "multiplier" can be calculated with the formula  where n is the number of Altars destroyed. So, destroying the 19th Altar would yield one-seventh of Cobalt/Palladium Ore compared to the first Altar. Destroying 12 altars will roughly double the ore provided by the first three; tripling that original allotment would require destroying 33 altars (if you can find that many).
 * Altars are needed for crafting certain items; destroying every Altar in a world is not recommended.
 * Destroying more Altars will never spawn Hardmode ore types beyond the three that were randomly assigned to your world during the initial round of destroyed Altars. A world with Palladium Ore deposits will never spawn Cobalt Ore deposits, or vice versa.
 * No matter how many Altars are destroyed, ore rarity remains set with Cobalt/Palladium being the most common, followed by Mythril/Orichalcum, then Adamantite/Titanium as the rarest.
 * Each time an Altar is destroyed, one or two Wraiths spawn, regardless of the time of day. When destroying multiple Altars in rapid succession, the resulting Wraith swarm may become difficult to deal with.
 * Each time an Altar is destroyed, there is a 66% chance that a single random stone block in the Caverns layer will be converted to Ebonstone/Crimstone or Pearlstone, facilitating the spread of underground Hallow or Corruption/Crimson. No block other than stone can be converted. If the game misses a stone block on its first try, it can try up to 999 more times before giving up.
 * Additionally, smashing an Altar will start spawning mechanical bosses (until it's defeated, each has a 10% chance of spawning each night), and random Pirate Invasions (if all the criteria are met).

Ore Generation
The amount of ore veins generated is determined by the formula (world size * 310 - (85 * ore tier)) * 0.85 / (amount of altars destroyed / 3 + 1) where  is the width of the world divided by 4200 (1 for small worlds, 1.5 for medium, 2 for large), and   is 0 for cobalt/palladium, 1 for mythril/orichalcum, and 2 for adamantite/titanium. The alternate ores added in 1.2 have their vein amount decreased by 10%.

The table below shows how many ore veins will be spawned for each altar destroyed. If 264 altars were to be destroyed in one world, all following altars would only spawn one ore vein.

* These values are for a small world. Multiply by 1.5 and 2 for medium and large worlds, respectively.

All hardmode ores will avoid spawning in the outer 100 tiles of the world. Cobalt and Palladium spawn from the Underground layer to 150 tiles above the world border. Mythril and Orichalcum spawn from the Cavern Layer to 150 tiles above the world border. Adamantite and Titanium start to spawn slightly lower than Mythril/Orichalcum. The heights they spawn at largely depend on the location of the underground boundaries in your world. See this section for specifics.

The amount of demon altars smashed does not affect the size of ore veins, only the amount. As the generation of each vein is heavily randomized, it is difficult to give exact high and low values from "optimal" veins. Instead, a table of "good luck" vein amounts and "bad luck" vein amounts is shown below. Average yeild is likely between 30-40% due to occasional lost ore.

Note however, that the above table assumes that all the ore actually replaces blocks. Should ore attempt to generate over any block not listed below, it will fail to generate, resulting in a smaller vein.

Hardmode ores won't generate over Granite Blocks, Marble Blocks, or any hardened sands, and as such cannot be found in the Granite Cave, Marble Cave, and Underground Desert biomes.

Hardmode Ore locations
* Small maps:
 * Cobalt Ore and Palladium Ore spawn below a depth of 760 feet (380 tiles)
 * Mythril Ore and Orichalcum Ore spawn below a depth of 1,000 feet (500 tiles)
 * Adamantite Ore and Titanium Ore spawn below a depth of 1,400 feet (700 tiles), 100 feet (50 tiles) above the depth at which Lava begins appearing
 * Medium maps:
 * Cobalt Ore and Palladium Ore spawn below a depth of 1,100 feet (550 tiles)
 * Mythril Ore and Orichalcum Ore spawn below a depth of 1,400 feet (700 tiles)
 * Adamantite Ore and Titanium Ore spawn below a depth of 2,130 feet (1,065 tiles), 170 feet (85 tiles) above the depth at which Lava begins appearing.
 * Large maps:
 * Cobalt Ore and Palladium Ore spawn below a depth of 1,270 feet (635 tiles)
 * Mythril Ore and Orichalcum Ore spawn below a depth of 2,000 feet (1,000 tiles)
 * Adamantite Ore and Titanium Ore spawn below a depth of 2,930 feet (1,465 tiles), 420 feet (210 tiles) above the depth at which Lava begins appearing.

Tips

 * It is not uncommon to find an Altar relatively close to the world spawn point. Wherever the player has set up their base, it is recommended to begin searching near 0 depth, and upon finding an Altar, build a room around it so the player can craft in relative peace.
 * Players about to enter Hardmode may benefit by mining paths to several known Altars beforehand, as navigating Hardmode Corruption/Crimson is dangerous at first.
 * Stacked Altars will bless the world with two ores when destroyed.
 * It is not strictly necessary to smash an altar; all ores obtained by doing so can also be obtained by fishing up crates, allowing access to all ores and their counterparts in one world.

Trivia

 * The difficulty that new players often face in identifying and determining the nature of Demon Altars, often resulting in forum posts asking about "purple spiky things", has become a notable social phenomenon in the Terraria community. A title message references this with the text 
 * In some rare cases an altar can spawn atop another altar. Hammering it in Pre Hardmode will deal damage and cause both altars to break.
 * Altars can spawn on sand. Breaking the sand beneath it will break it, but ores will spawn only in Hardmode.
 * In some rare cases an altar can spawn on top of a Crystal Heart. Both lower quarters of the heart can be collected as two separate items, but the top half stays unbroken under the altar. The remaining half still exhibits its normal animation after the bottom half is broken.
 * A wraith is defined as a spirit seen shortly before or after one's death; their appearances when an altar is broken may imply that altars are indeed living creatures.

History
Autel Altar 祭坛