Altars

Demon Altars and Crimson Altars are naturally-occurring crafting stations found mainly in and around Chasms in The Corruption or The Crimson, and more rarely in other areas 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 that causes the player to lose half their health, and the Altar will not be affected.



Hardmode
After the Wall of Flesh has been defeated in a world, Altars can be destroyed with the Pwnhammer or any superior hammer. Each destroyed Altar 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)". 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.


 * 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.


 * Destroying a fourth Altar spawns another round of whichever type spawned for the first Altar (Cobalt or Palladium). A fifth spawns more of whichever type spawned for the second Altar (Mythril or Orichalcum), etc.
 * 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.
 * 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.
 * Which ores are generated is not determined until you smash an Altar. For example, it is not determined which ore your world has cobalt or palladium, until the first altar has been smashed. The same goes for Mythril/Orichalum with the second altar, and Adamantite/Titanium for the third.
 * In addition to spawning new ore, a small patch of Corruption, Crimson, or Hallow have a chance to be seeded at a random world location.
 * Additionally, smashing an altar will start spawning mechanical bosses randomly at night, and will start to trigger Pirate Invasions.

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 1,000 depth (500 tiles)
 * Adamantite Ore and Titanium Ore spawn below 1,400 depth (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 1,400 depth (700 tiles)
 * Adamantite Ore and Titanium Ore spawn below 2,130 depth (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 2,000 depth (1,000 tiles)
 * Adamantite Ore and Titanium Ore spawn below 2,930 depth (1,465 tiles), 420 feet (210 tiles) above the depth at which Lava begins appearing.

Achievement
Begone, Evil! is the achievement you earn when you smash your first Demon Altar or Crimson Altar.

Tips

 * Players about to enter Hardmode may benefit by mining paths to several known Altars beforehand, as navigating Hardmode Corruption/Crimson is dangerous at first.
 * Altars are still needed for crafting certain items, and altars yield fewer ore with every group of three destroyed. Destroying every altar in a world is not recommended.
 * On the rare occasion that an altar spawns on top of a Heart Crystal, the bottom two portions of the crystal can be broken for two separate items, while the top two portions remain unbreakable.

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 Terraria: What's that purple spiked thing?
 * In some rare cases a altar can spawn on other altar.