Refer to the passage below and then answer the question afterwards in the same language as the passage:

Passage: The first Europeans in the area were Spanish explorers in 1516. The Spanish explorer Juan de Salazar de Espinosa founded the settlement of Asunción on 15 August 1537. The city eventually became the center of a Spanish colonial province of Paraguay.

Question: When was the settlement founded?
15 August 1537