Friday will mark 25 years since the World Trade Center attacks on Sept. 11, 2001. Between the attacks themselves, the lasting health impacts on survivors and ensuing wars, the death toll for Americans is in the tens of thousands.

The milestone anniversary brought memorial rituals — wreath-laying, flag-flying, moments of silence, vigils and readings of victims’ names — and volunteer projects in tribute to a day that about half of U.S. adults remember as the most historic event of their lifetime.