Raised under King Mahasena in the third century CE, and when complete one of the tallest brick structures ever built anywhere — originally over 120 metres.
The engineering is the remarkable part. The foundation had to carry an enormous mass of brickwork on soil that would not naturally bear it, and the builders solved this with a compacted base and a brick specification consistent enough that modern analysis has been able to estimate its load tolerance. Estimates of the brick count run to the tens of millions.