The Pyramid of Djoser in the Saqqara necropolis complex predates Silbury by about 300 years (I think). It’s similarity to Silbury is interesting because it has six mastabas of decreasing size (Silbury has five I think). The inner core of Djoser, like Silbury, consists of rubble and was originally ‘clad in polished white limestone’. It’s tempting to think there’s a connection, especially as there’s a word in ancient Egyptian that closely resembles the word ‘Kennet’ and means the ‘fertile lands’. I keep loosing that last bit of info so if anyone has it and can repost it here I’d be grateful.