They have left behind them testimonies of the satisfaction they found in each other’s acquaintance.  “For my part, says Grotius in a letter to John Frederic Gronovius[62], I reckon it one of the greatest felicities of my whole life to have been loved by a man as illustrious for his piety, his probity, and his candor, as for his extensive learning.  It was by his counsels or those of persons he approved that I conducted myself in the most difficult times.”

“I respect no less, says he in another letter, his frankness and his probity, than his uncommon erudition.  His letters sufficiently prove what great friendship he had for me.”

We find in fact that they contain evidences of the highest esteem for Grotius.  To Daniel Heinsius he writes, April 13, 1613, “I am very well; and cannot say enough of my felicity in enjoying the friendship of such a great man as Grotius.  O that incomparable man!  I knew him before:  but fully to comprehend the excellency of his divine genius, one must see him, and hear him converse.  His countenance speaks probity, and his discourse discovers the deepest learning and the most sincere piety.  Think not that I only am his admirer; all learned and good men entertain the same sentiments for him, particularly the King.”

Casaubon writes to the President de Thou, April 20, 1613, to acquaint him what pleasure he had received by seeing Grotius.  “I must let you know, says he, that I have seen here Hugo Grotius.  He is a man of admirable probity and learning[63].”

They had long conversations together on religion.  Casaubon ardently desired a reunion of the Protestants with the Roman Catholics[64]:  and would have set about it, had he staid longer in France, as he informed Descordes, who repeated it to Grotius.  He greatly respected the opinions of the ancient church[65], and was persuaded its sentiments were more sound than those of the Ministers of Charenton.  Grotius and he had imparted their thoughts to each other before the voyage to England:  for Casaubon congratulates him, January 8, 1612, on his desiring nothing but peace and a coalition; and communicated Grotius’ sentiments to King James; who approved of them.  This shews that Grotius thought it was wrong to depart from the discipline and forms of the ancient church:  Casaubon was of the same mind; and his Letter to M. de Thou is a demonstrative proof that these two excellent men did not differ in matters of Religion.  “I esteem him highly, says he[66], on account of his other great qualities; for he judges of the modern subjects of religious controversy like a learned and good man; and in his veneration for antiquity agrees with the wisest.”

The last Letter which we have from Casaubon to Grotius comprehends all these sentiments in few words[67]:  “I heartily pray God to preserve you ever:  and as long as I live, I shall hold you in the highest esteem, so much am I taken with your piety, your probity, and your admirable learning.”