Gerard Vossius speaks of him as the greatest poet of his age, and the prince of poetry.

In fine, M.Baillet, who had examined the many opinions given of Grotius, assures us, that all who read his poems approved of them; that those of fine taste, and who could judge of epigrams, found many of his admirable, some discovering the subtilty of his genius, and the fertility of his imagination; others, the happy turn which he could give to his thoughts and expressions.
Even his enemies did not presume to deny him the praise of an excellent Poet; and Salmasius, in a letter written with design to lessen Grotius's reputation, and dictated by jealousy, injustice, and spleen, allows however he was a great Poet.

"But," he adds, "every one in this country prefers Barlaeus; and many, even Heinsius." Balzac, who in other things did justice to Grotius, wished he had employed his poetic talents only on proper subjects.

"I never saw," says he, "the Swedish Ambassador, but I have long esteemed his genius: and if he had not put the _Institutes_ into verse, and published some other pieces of the same nature, I should esteem him still more." But it is proper to observe that these were the amusements of his childhood, and never intended to be made public.
Grotius had a meaner idea of his poetical talents, than even the rivals of his glory.

"As to merit in poetry (he writes to the President de Thou) I yield it to every one." It was William Grotius who published the collection of his brother's poems.