Actually, if Moses flourished around 1800 BC, he was contemporaneous with the building of the last known pyramid, the pyramid of Amenemhet III.
Of course, the golden age of pyramid building was 800 years before Moses - the time when the Great Pyramid of Khufu at Gizeh was built. Khufu's was almost six times the size of Amenemhet III's.
But in Moses' time there were vast public works projects that would have dwarfed that particular gravesite in scale and importance.
The usual dating for Moses is well after 1800.
If the Biblical chronology placing Moses at 1200 BC is correct, it would place Moses 500 years after the last documented pyramid project.