World 2 · The Roman Arch and the Keystone · 10 min · PRO
Why build an arch?
Stone is strong when squeezed, weak when stretched
PRO · Ancient Engineering
World 2: The Roman Arch and the Keystone is part of PRO
The first world of Ancient Engineering is free. PRO opens the other 24 lessons in 6 worlds — simulations, quizzes and all.
PRO includes
- All 60 labs — every world, every lesson
- Practice exams and certificates
$8.33/mo, billed yearly ($99.99) · or $39.99 monthly