・In 1562, Yokoseura Port was opened as a port for trade with Spain and Portugal. Foreign merchants entering the port by Portuguese ships were allowed to be free from customs duty for 10 years. People of different religions were prohibited from living on and around the grounds of the port without permission from the church priest. It was determined that half of the areas within a radius of about two leguas (1 legua was approximately 5.5 km) should be possessed by the church.
・A church was constructed in Yokoseura, where many Christians and merchants gathered, and the port enjoyed prosperity. In 1563, Omura Sumitada, the feudal lord of the Omura domain, was baptized and became the first Christian feudal lord in Japan.
・In the same year, however, Yokoseura Port was attacked by anti-Sumitada forces and burned down. Later, the port for trade with Spain and Portugal was transferred to Fukuda, and then to Nagasaki.
・Today, the place where a church is considered to have been constructed has been developed as a park. The experimental learning facility of the park provides an introduction to the history of Christianity in Saikai City.