Altars are used to increase ninja stats permanently. When you first build it increases hp and attack of class ninjas. You need altar stones to increase upgrade. Upgrade level is capped by building level.
There are 3 altars, one for every ninja class.

Here is a table with levels and strenght given.

Level 1 2 3 4 5 6 7 8 9
File:Altar stone.png free 2 4 8 12
File:Tai icon.png Attack 68 83
Hp 324 422
File:Weapon icon.png Attack 45 59
Hp 259 338
File:Nin icon.png Attack 65 84
Hp 227 295

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