In the context of piaget's stages of cognitive development, are mental representations that are reversible.

- "sack of constantinople, (april 1204). the diversion of the fourth crusade from the holy land to attack, capture, and pillage the byzantine city of constantinople divided and dissipated the efforts of the christians to maintain the war against the muslims. the fourth crusade was corrupted from its purpose early on."

- "the crusades were a series of religious wars undertaken by the latin church. the first crusade arose after a call to arms in 1095 sermons by pope urban ii. the first crusade unleashed a wave of impassioned, pious catholic fury, which was of constantinople, the capital of the christian-controlled byzantine empire."

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