The military-backed government inaugurated the monument Monday in a ceremony dedicated to both those who died during the 2011 uprising, as well as those killed in June's overthrow of President Mohamed Morsi.
Just hours after the pedestal was unveiled by Egypt's interim prime minister, it had already been defaced by protesters who marched on the square.
The approximately 1,000 protesters ripped off the plaque bearing the names of Egypt's current ministers, replacing it with their own messages, Reuters reported.
According to the Associated Press, one large message said: "Down with all traitors: army, old regime and the Brotherhood."
"A word in your ear, Sisi, don’t dream of being my president!" the protesters reportedly chanted as they rallied in the streets.
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The monument comes, not coincidentally, just a day before the anniversary of some of the worst violence during the uprising against long-time leader Hosni Mubarak in 2011.
Some activists see the move as an attempt by the new military government to re-write history, painting the Egyptian armed forces in a better light despite their involvement in the deaths.
Rallies are expected on Tuesday to mark the anniversary of the violence in Tahrir. Last year, similar rallies turned into clashes between police and demonstrators.