Also, the city is in the Nile Delta area. The ground was “sinking sand” to begin with, since the river constantly deposits silt, shifts its channel, and generally restructures the topography all the time. Add in earthquakes and storms, and a nice port city can easily be left submerged, like Caesaraea Maritima, or high and dry.
Think of New Orleans and the Mississippi Delta area or the river-mouths area we call Bangladesh. It doesn’t take sea-level changes to make the situation unstable.
Is that what happened in Detroit ? Heard that they are underwater too.
Yes. Any area with any depth of sediments is vulnerable. The New Madrid (MO) earthquake(s) were an excellent example (and will be again).