A unit assembled brick, comprising: four first linkage bricks, each comprising a top face, a bottom face and four side faces (313, 314, 315, 316) between said top face and said bottom face, each of said side faces forming a traverse engaging groove (3131, 3141, 3151, 3161) extending laterally; four second linkage bricks each comprising a top face, a bottom face and four side faces (323, 324, 325, 326) between said top face and said bottom face, each of two opposite side faces (323, 325) of said side faces forming a traverse engaging protrusion (3231, 3251) extending laterally, and each of the other two opposite side faces (324, 326) of said side faces forming a vertical engaging protrusion (3241, 3261) extending vertically; and a third linkage brick comprising a top face, a bottom face and four side faces (333, 334, 335, 336) between said top face and said bottom surface, each of said side faces forming a vertical engaging groove (3331, 3341, 3351, 3361) extending vertically, wherein a top face (32411, 32611) and an outer side face (32412, 32612) of each of said vertical engaging protrusions (3241, 3261) of said second linkage bricks defines a wedged corner, and each of said vertical engaging grooves (3331, 3341, 3351, 3361) of said third linkage brick correspondingly forms a wedged grooved portion, wherein said first linkage bricks engage with said second linkage bricks alternately, adjacent traverse engaging grooves (3131, 3141, 3151, 3161) of said first linkage bricks engage with adjacent traverse engaging protrusions (3231, 3251) of said second linkage bricks to form a hollow square ring that is arranged into a 3x3 array, and inner sides of said square ring have four vertical engaging protrusions (3241, 3261) of said second linkage bricks, wherein said third linkage brick is placed in the center of said hollow square ring and each of four vertical engaging grooves (3331, 3341, 3351, 3361) of said third linkage brick respectively engages with each of four vertical engaging protrusions (3241, 3261) of said second linkage bricks facing said inner sides of said square ring, and wherein said wedged corner of each of said vertical engaging protrusions (3241, 3261) of said second linkage bricks engages with said wedged grooved portion of each of said vertical engaging grooves (3331, 3341, 3351, 3361) of said third linkage brick. four first linkage bricks, each comprising a top face, a bottom face and four side faces (313, 314, 315, 316) between said top face and said bottom face, each of said side faces forming a traverse engaging groove (3131, 3141, 3151, 3161) extending laterally; four second linkage bricks each comprising a top face, a bottom face and four side faces (323, 324, 325, 326) between said top face and said bottom face, each of two opposite side faces (323, 325) of said side faces forming a traverse engaging protrusion (3231, 3251) extending laterally, and each of the other two opposite side faces (324, 326) of said side faces forming a vertical engaging protrusion (3241, 3261) extending vertically; and a third linkage brick comprising a top face, a bottom face and four side faces (333, 334, 335, 336) between said top face and said bottom surface, each of said side faces forming a vertical engaging groove (3331, 3341, 3351, 3361) extending vertically, wherein a top face (32411, 32611) and an outer side face (32412, 32612) of each of said vertical engaging protrusions (3241, 3261) of said second linkage bricks defines a wedged corner, and each of said vertical engaging grooves (3331, 3341, 3351, 3361) of said third linkage brick correspondingly forms a wedged grooved portion, wherein said first linkage bricks engage with said second linkage bricks alternately, adjacent traverse engaging grooves (3131, 3141, 3151, 3161) of said first linkage bricks engage with adjacent traverse engaging protrusions (3231, 3251) of said second linkage bricks to form a hollow square ring that is arranged into a 3x3 array, and inner sides of said square ring have four vertical engaging protrusions (3241, 3261) of said second linkage bricks, wherein said third linkage brick is placed in the center of said hollow square ring and each of four vertical engaging grooves (3331, 3341, 3351, 3361) of said third linkage brick respectively engages with each of four vertical engaging protrusions (3241, 3261) of said second linkage bricks facing said inner sides of said square ring, and wherein said wedged corner of each of said vertical engaging protrusions (3241, 3261) of said second linkage bricks engages with said wedged grooved portion of each of said vertical engaging grooves (3331, 3341, 3351, 3361) of said third linkage brick.