[Pope Francis, pictured here during a visit to Mexico's border with the US, highlighting the plight of migrants, will visit Lesbos in Greece later this week, which is at the frontline of the Europe's migrant crisis]Pope Francis called on Catholics worldwide Wednesday to pray for his upcoming trip to the Greek island of Lesbos, on the frontline of Europe's migrant crisis, saying he wanted to show "solidarity" with the refugees and the Greek people.