[G 12 / Mongol] attacks from the northeast had indicated defense weaknesses and in 1551 work began on the defenses east of Beijing, which itself received a new wall in 1533. To the west of the capital, building and repairs to existing walls took place too.
Proposals to repair existing towers and build new ones to the south were made in 1556. In 1557 and 1558 more repair work was carried out in [M 004 / Shaanxi] and the Datong wall, among others. Extensive fortificaton work was conducted from 1567 to 1573 and on into the 17th century. In 1565 Shanhaiguan was strengthened. The most important work was, however, considered to have been on the northeastern frontier.
