So, I guess, pyramid-building; that's a collective project spanning a few centuries. I struggle to think of any collective project that spans centuries, that isn't fundamentally a religious enterprise.
> In the Western world, 66 institutions have enjoyed a continuously visible identity since 1530. Among those 66 are the Roman Catholic Church, the Lutheran Church and the Parliaments of Iceland and the Isle of Man. What makes these 66 so interesting —and I owe the knowledge of this fact to our President Dr. Berdahl— is that the remaining 62 are all universities!
It depends a bit, I think, on how much drift you accept without considering the project to have changed so much it's not the same thing. But for instance some of the older universities in Europe are pretty much the same institutions working on the same goal (educating people) in the same buildings for many hundreds of years. The details of what the education provided ought to be, the balance between education and research, and the administrative details have changed quite a bit, but I think you can still make a case for this being the same non-religious collective project.
> I struggle to think of any collective project that spans centuries, that isn't fundamentally a religious enterprise.
Certain parts of mathematics and science may qualify.
Yes they have practical outcomes (as do certain religious projects - building a cathedral will employ craftsmen), but isn't the pursuit of 'pure' mathematics a collective project which serves no purpose apart from intellectual satisfaction.
Maths has a constant "next step" which makes it very iterative though whereas a pyramid or a cathedral is only complete or not-complete, and it's not-complete over these decades/centuries.
Maths requires a huge amount of creative effort and there often is no logical next step. There was a reason that it took three hundred years to go from an idea that a^x + b^x = c^x has no integer solutions when x is greater than two, to a proof of that, and it involved some crazy twists and turns of thinking.
However, while a pyramid may have a definite endpoint, cathedrals have historically been in a near constant state of flux - a bishop wants to show his influence and rebuilds a tower higher, a burgher of the town want to show his power by adding a side chapel. New windows are installed, a porch is demolished and replaced with something more beautiful. For the cathedrals which took five hundred years to complete, it wasn't that they were abandoned building sites during that time - they just took that long to reach the state that we see as final today. Maybe in-between there was a wooden roof instead of a stone roof, or a tower was capped at thirty meters tall rather than fifty!
+ the original meaning, not the internets one, which is only an extremely short-lived subset.