The Silla Pirates Who Invaded Japan (“Sillagu,” 新羅寇)

1. Overview

Around the 9th century, near the end of Unified Silla, groups of Silla pirates based along the Silla coast raided Tsushima and parts of Kyushu. Japanese historical records refer to these attacks as “Silla invasions” (新羅の入寇) or “Korean invasions” (韓寇).

These pirate activities reportedly caused mounting damage in Japan and led the Japanese court to restrict Silla immigrants and naturalization. However, accounts of the Silla-gu are almost absent from Korean historical sources and are concentrated in Japanese records, so various interpretations exist regarding their actual scale and who was behind them.

2. Background to the Emergence of the Silla-gu

Near the end of Unified Silla, abuses of the bone-rank system worsened, weakening the central government’s control over the provinces. Bandits, thieves, and pirates proliferated across the country. One claim holds that refugees from the former Baekje region turned to piracy, and accounts also say they sold Silla people into slavery. Later, Jang Bogo established Cheonghaejin around Wando and suppressed the pirates, making piracy difficult within the Korean Peninsula.

The pirates then sought out areas beyond Jang Bogo’s jurisdiction that offered good targets; according to one claim, Japan became such a target. At the time, Japan was in the mid-Heian period. The ritsuryō system had weakened, central government control was lax, and the western regions were reportedly poorly defended.

3. Damage to Japan’s Coast

The Japanese historical record Nihon Kōki states that in December 811, about 110 Silla people invaded Ojikashima (小近島) in five ships, killing about nine people and capturing 100. The same month, more than 20 Silla ships reportedly landed on the Satsuura coast of Kyushu. Nihon Kiryaku also records that in March 813, 110 Silla people arrived in five ships and landed on Ojikashima in Hizen Province, where they fought the local residents.

In February 820, 700 Silla people who had been relocated to the provinces of Tōtōmi and Suruga reportedly rebelled, killing residents and setting houses on fire. The two provinces mobilized troops but could not suppress the rebellion. After forces were gathered from seven provinces and sent to put it down, all the rebels reportedly surrendered. The incident is said to have intensified anti-Silla sentiment in Japan.

A record states that in May 869, Silla pirates arrived at Hakata Port in two ships and plundered silk and other goods offered as tribute. The court, informed of the incident, recorded that the Silla pirates had invaded in search of an opportunity amid political instability. Afterward, the term “Silla-gu-do” (新羅寇盜), referring to the Silla-gu, appears in historical records.

There is a record that Silla pirates invaded Hizen Province and burned homes in 893. The following year, in September 894, Fusō Ryakki states that 45 ships belonging to a group of Silla bandits arrived in Tsushima. According to the same record, the captured pirate Hyeonchun reportedly spoke of famine in Silla and financial hardship at the royal court, and claimed that the group’s base had 100 ships and 2,500 troops.

4. Restrictions on Silla Immigration and Naturalization

Some accounts hold that, as these raids continued, the Japanese court established laws restricting Silla immigration and naturalization, and relocated Silla people who had already naturalized to eastern regions. One explanation for the resulting concentration of families descended from Silla immigrants in eastern Honshu is this relocation.

Some view this period as a turning point that curtailed Japan’s foreign relations and helped foster its national culture. However, this is generally interpreted as the result of multiple overlapping factors, rather than the influence of the Silla-gu alone.

5. Authenticity Debate

There are two central points of debate: whether the Silla-gu were pirates acting independently of the Silla government, and whether Japanese accounts of the events were exaggerated or biased.

5.1. The View That They Were Independent Pirate Groups

The basis for this view is that Japanese historical records describe Silla-gu raids with relatively specific dates and numbers. Similar accounts of these events appear repeatedly in several records, including Nihon Kōki, Nihon Kiryaku, Nihon Sandai Jitsuroku, and Fusō Ryakki. The appearance of ranks such as “great general” and “vice general,” as well as references to fleets of 100 ships, is also cited as evidence of organizational capacity beyond that of ordinary civilian pirates.

5.2. The View That They Cannot Be Considered Unconnected to the Silla Government

The opposing view points to the Silla-gu’s use of the Silla coast as a base and to a statement in a prisoner’s testimony that some of the forces had been supported by the Silla king, raising the possibility of state involvement. A counterargument is that the reliability of this testimony is also difficult to verify given the nature of the record. The near absence of accounts of the pirates in Korean sources is another point of disagreement. The absence of Silla-side records does not mean the Silla-gu did not exist; it is also possible that Silla did not officially document them or that such records have not survived.

6. Trivia

• Some point out that the term “Silla-gu” itself follows the naming pattern of “Wokou” (倭寇), and was not used as such in Japanese historical records, but was adopted by modern researchers and the media as they organized accounts of the events.
• The Silla-gu story became known to the Korean public when KBS1’s History Tracking aired “Silla Pirates: Why Did They Invade Tsushima?” in 2008.