How did they build this?

Brief, grounded studies of remarkable structures around the world — what they are, how they were made, and the questions still left open.

Chand Baori
With no surveying instruments beyond simple tools, how did builders lay out roughly 3,500 steps in a repeating, symmetrical geometric pattern descending 13 storeys to the water table without a single visible error, and how much of what stands today is the original 8th-9th century core versus later rebuilding?
c. 8th-9th century CE · Abhaneri, Dausa District, Rajasthan, India
Göbekli Tepe
How did hunter-gatherers with no metal tools, pottery, or agriculture organize the labor to quarry, move, and raise multi-ton carved pillars, and why?
c. 9600-8000 BCE (Pre-Pottery Neolithic) · Şanlıurfa, Southeastern Anatolia, Turkey
The Kailasa Temple
How was an entire multi-storey temple carved top-down from a single rock, with no room to correct a mistake?
c. 757-783 CE (reign of Krishna I) · Ellora, Maharashtra, India
Newgrange
How did a farming community without writing, metal tools, or (as far as the evidence shows) any recorded mathematics engineer a 19-meter passage to funnel winter-solstice sunrise into a chamber with such precision, and what did the tomb mean to the people who built and used it?
c. 3200-3100 BCE (Neolithic) · Brú na Bóinne, County Meath, Ireland