Pope Francis has beatified 124 Christian "martyrs" in the South Korean capital, and challenged Christians on the values they may be willing to die for in an increasingly materialistic and globalised world.
The pope performed the beatification on Saturday at a mass in front of hundreds of thousands of Catholics in Gwanghwamun plaza, Seoul's main ceremonial thoroughfare.
The Koreans were killed in the 18th and 19th centuries for refusing to renounce Christianity. Francis said their courage, charity and their rejection of the rigid social structures of their day were an inspiration for people today.
"Their example has much to say to us who live in societies where, alongside immense wealth, dire poverty is silently growing," he said.
The most prominent among those beatified was an 18th century nobleman, Paul Yun Ji-chung, who became Korea's first Catholic martyr when he was executed in 1791 after clashing with Confucian officials.
"They knew the cost of discipleship... and were willing to make great sacrifices," Francis said in his sermon after the brief beatification ceremony, which gives the martyrs the title "blessed" and marks their first step towards sainthood.
According to the Church, around 10,000 Koreans were martyred in the first 100 years after Catholicism was introduced to the peninsula in 1784.
Francis has been vocal in his criticisim of materialism since arriving in South Korea, a theme that has underscored his papacy.
Last year, in his first major written work, Francis attacked unfettered capitalism as "a new tyranny", urging global leaders to fight poverty and growing inequality.
Rapid economic growth has made South Korea one of the world's wealthiest countries, but it has also become increasingly unequal, with nearly half the elderly in poverty.
The Catholic Church has a fast-growing presence in South Korea, doubling in the past 25 years to about 11 percent of the population, adding about 100,000 new members every year.