Arrange the steps by which agricultural change supported urban growth.

1. Heavier ploughs and better traction open new and wetter soils
2. Three-field rotation raises the share of land under crop each year
3. Food output rises faster than the labour needed to produce it
4. Population not required on the land concentrates in towns
5. Towns purchase charters granting markets, courts and tolls

The last step is the one that is easy to skip. A town’s liberties were usually bought or negotiated, not granted out of goodwill: a lord sold rights for cash he needed, and the community could pay because the surplus at step three had made it rich enough to.