There is no beginning or end date for medieval London. Long-term changes transformed the post-Roman city into a 16th-century metropolis. Crown and church worked with city institutions to manage the outcome, but economic, social, geographic, and demographic factors beyond their control were the determinants of London’s evolution. Medieval London owed much to a well-chosen Roman site with double-facing connectivity, providing access to mainland Europe by sea and to the interior by river. London was the lynchpin. The Roman settlement had a defensive fort and walls, an amphitheater—recently rediscovered underneath the medieval Guildhall–and an impressive road network converging on the city. This defensible hub, combining economic prosperity with popular entertainment, was the basis for London’s perennial appeal to English and alien migrants. It quite literally provided the foundation for medieval London. The early extramural Anglo-Saxon settlement relocated behind the walls as an Alfredian burh, expanding trade with nearby parts of the Continent. The Norman construction of the Tower, overshadowing the eastern aspect, demonstrated that control of London was essential to government of the realm. An economic driving force, the city was not the administrative capital until the 12th century. London generated trade revenues and ensured urban stability, in return for which the Crown granted self-government and privileges for its merchants and markets. The city’s own records survive from the later 13th century, although its institutions have earlier origins. Regarding itself as the New Troy, it engaged in public works and staged triumphant royal entries. London’s bread-basket extended to the Norfolk coast and the upper Thames valley. Apart from frank discussions at the wardmote, there were further opportunities for ordinary Londoners to express their views and participate. The craft guilds regulated the city’s trades and their members, developing separate livery and yeomanry organization. Parish fraternities were a neighborhood outlet for literate lay spirituality and accounting skills. The population, significantly reduced by the Black Death, recovered and prospered. London was above all a cosmopolitan city with thriving markets and accessible credit. Although there were recurrent demands for protection against alien competition, aliens joined the livery companies, became citizens of London and some became Englishmen. The royal Court, Parliament, and law courts a short ride away at Westminster guaranteed good business for city merchants. Most importantly, the lucrative 14th-century wool trade and 15th-century cloth trade were increasingly concentrated in the hands of Londoners who dominated English exports.