China had been impressed with "red-barbarian cannon" since around 1600, when an enormous specimen was procured from some European ship. Paul Xu—a Jesuit convert who rose to very high office in large part due to the superiority of Western geometry, with its applications in astronomy, astrology, and accurate use of artillery—warmly encouraged the use of Portuguese guns to counter the ongoing Manchu invasions of northern China. However, during Corrêa's time in China, there was debate among the mandarins as to whether the Manchus in the north or the increasing numbers and violence of European traders in the south were actually the greater threat. Shen Que, a Buddhist adept who rose to prominence in the Ministry of Rites, had succeeded in having the Jesuit mission in Nanjing expelled and its property confiscated in 1616 and Lu Zhaolong, a native of the Guangdong county on the mainland opposite Macao, published memorials heatedly arguing against permitting the "South-Sea barbarians" any access to China whatsoever. The competition of the factions was apparent when Xu succeeded in having a company of Portuguese gunners approved in 1620 only to have them returned the way they'd come in 1621, owing to local resistance upon various pretexts. After the fall of Guangning (now Beizhen in Liaoning), Ignatius Sun's extremely thorough memorials on the superiority of Western cannon and fortification attracted attention at the highest levels of the War Ministry. The Tianqi Emperor permitted a second Portuguese expedition to reach his capital in the spring of 1622. The same year, a Dutch assault on Portuguese Macao was repulsed when a gunner and the geometrician Giacomo Rho successfully struck the exact spot of the Dutch powder stores. The delegation in Beijing was sent home in 1624, however, when an exploding cannon killed the gunner João Corrêa and his two Chinese assistants.