[Paal Gulli]

As brilliant a piece of engineering as it is, it still bears proof to the old axiom, "The best laid plans of mice and men, oft go astray." Something you might never have noticed if you've only seen it from ground level.

See the "chevron" on the wall above the roof of the portico (indicated by arrows)? That's where the designer intended the portico's roof to have come to.

So why doesn't it? Nobody knows. But the columns are mismatched, too, different diameters, different styles, and made from stone from different quarries. Which gives rise to speculation that the original columns never arrived so the builders had to make do with whatever they could scrounge. They were supposed to have been quarried in Egypt, and the majority of the shipping route to Rome would have been over water, and shipwrecks were a common occurrence. Maybe pirates. Maybe Egyptian bureaucracy, who knows?

[SunkenCiv]

I’ve often wondered if the portico was either changed, or as it was the last thing constructed, there was a budget problem, maybe that whole part was available from another project, so they used that. Perhaps the portico survived from the original version, which was largely wood construction.