Sailly, Thomas, a Belgian theologian, was born at Brussels in 1553, where he died in 1623. At the age of seventeen, having been already ordained priest, he went to Rome to enter the Society of Jesus. When hardly out of his novitiate, he was sent by Gregory XIII on an embassy to the czar Ivan. On account of his health he was recalled, and became confessor to prince Alexander of Parma. In 1597 he was made superior of a military mission, and in 1606 he went to Rome as procurator-general of the Belgian provinces. In 1620 he took part as missionary in the campaign of Spinola. He was the author of works in Latin, Flemish, and French: Guidon et Pratique Spirituelle du Soldat Chretien (1590): — Narratio Itineris Fr. de Mendoza, Almirantii Aragonioe, in Leqatione sua (1598): — Thesaurus Litanarum ac Orationum Sacer (1598): — Den niewen Morghenwekker (1612). He also translated several religious treatises into his native language.