liner notes from Gallicantus's third cd release describe the exchange:
The connection that brings together the music of William Byrd (c.1540-1623) and Philippe de Monte (1521-1603) is a most unusual one: a very rare documented instance of two composers from distant parts of Europe engaging in a personal musical exchange. According to an 18th-century manuscript in the British Library, de Monte had come to England in 1554 as a singer in the choir that accompanied his employer, the Spanish king Philip II, as he contracted a dynastic marriage to Mary Tudor. It seems that de Monte may have made contact with the young William Byrd, for some 30 years later he sent him the eight-part motet Super flumina Babylonis, and the following year, Byrd responded with his own eight-part Quomodo cantabimus, whose words are drawn from verses of that same psalm, no. 136. Exactly what occasioned this musical transaction is not known, but the words must have held particular resonance for Byrd at that time, as this famous psalm of captivity and exile would surely be interpreted as a barely veiled allusion to the dangerous situation that he and his fellow recusant Catholics were facing under a Protestant regime in England at a time when political tensions were aggravating the existing religious ones; perhaps word of these developments had reached de Monte, either in Prague or via his benefice at Cambrai, near the Catholic English College at Douai.
The CD is available from Signum Classics and the website highlights the key to the hidden meaning of Byrd's setting of these texts: "The texts reveal the Catholic community’s sense of isolation (“How shall we sing the Lord’s song in a strange land?” – Quomodo Cantabimus) and bereavement (“Jerusalem is wasted” – Ne Irascaris), and the elaborate, poetic nature of the encoded messages distributed within it through music.'