How do you know they're aligned north-south?
In fact, they could be aligned east-west (which makes more sense in the cultural context.) There are many examples of tombs and temples aligned to the rising sun on a specific date.
It's extremely easy to get a north-south-east-west alignment:
On the morning of the equinox (or as close as you like or use the date you prefer), take a stick, poke it in the ground, mark along the shadow. You now have a perfect east-west line and since they knew how to make a right angle tool, lay one of those on your line and you now have a perfect north-south alignment.
