Lodewijk Heyligen (also known as Ludovicus Sanctus de Beeringhen, Lodewijk Heiligen, Ludovicus Sanctus, Heyliger of Beeringhen, Ludwig van Kempen and Louis van Campen) (1304, [[Beringen, Flanders ]] – 1361, Avignon) was a Flemish Benedictine monk and music theorist who served as the master of music of cardinal Giovanni Colonna in Avignon.
In a letter to the chapter of the St. Donatian's Cathedral dated 27 April 1348 the content of which has been partially preserved, Lodewijk Heyligen describes the horrors of the plague that was then raging in Europe.
He ascribes the origin of the plague to calamitous events in India and the arrival in Genoa and later Marseille of merchant ships coming from the Orient.
Only in 1904 was it established with certainty on the basis of documents from the Vatican that the person to whom Petrarch in his writings referred as 'Socrates' was in fact Lodewijk Heyligen.
It is possible that Lodewijk Heyligen inspired in Petrarch the desire to visit the Southern Netherlands (present-day Belgium), a trip that the two friends may have taken together.
Petrarch dedicated the collection entitled Epistolae de rebus familiaribus (Familiar Letters) to his friend referred to as Socrates.
A note in his Virgil-codex reveals his sadness upon receiving the news of his death: "Amisi comitem ac solatium meae vitae" (I have lost my comrade and the solace of my life!).
Petrarch also called up the memory of his friend in a passage in the Trionfo d'Amore (Triumph of Love, from Triumphs) where he recognizes Socrates and Lelio (the literary nickname of Stefano Romano, a mutual friend of Petrarch and Lodewijk) amid the crowd, which is carried behind the chariot of Cupid: Poco era fuor de la comune strada, quando Socrate e Lelio vidi in prima: con lor più lunga via conven ch'io vada.
Con questi duo cercai monti diversi, andando tutti tre sempre ad un giogo; a questi le mie piaghe tutte apersi; da costor non mi pò tempo né luogo divider mai, siccome io spero e bramo, infino al cener del funereo rogo; con costor colsi 'l glorïoso ramo, onde forse anzi tempo ornai le tempie in memoria di quella ch'io tanto amo.