What do you need in order to watch the sky steadily?

That time, that place

In Gyeongju, the Silla capital, stands a 9.17-metre tower built from some 362 stones, raised in 647 under Queen Seondeok.

What it was for is still argued: an observation platform, a ritual structure, or a symbol.

Why this question

Start with what is certain. Watching the sky steadily needs three things: the same spot each time, a note of when you looked, and a way to hand the notes on.

A telescope is optional. A fixed place and a continuous record are not.

What was found

The Samguk Sagi lists eclipses, comets and stellar anomalies with dates attached, and the density of those entries shifts around the time the tower went up.

Whatever it was for, Silla began recording the sky systematically in this period. And those records are still read: ancient eclipse timings are used today to confirm that the Earth's rotation is very gradually slowing.