In the year 1608, while he held the office of Advocate-General, Grotius composed his ‘Mare Liberum,’ the general design of which was to show, upon the principles of the law of nations, that the sea was open to all without distinction, and to assert the right of the Dutch States to trade to the Indian seas, notwithstanding the claim of the Portuguese to an exclusive title to that commerce. This tract was published without the consent of Grotius; and at a subsequent period of his life he expressed his disapprobation of it. “My intention,” he says, “was good; but the work savours too much of my want of years.” Many years afterwards, Selden published his profound work on maritime rights, entitled ‘Mare Clausum,’ in which he incidentally notices this treatise of Grotius with much respect, though he advocates a contrary doctrine. Soon after the appearance of his ‘Mare Liberum,’ Grotius published a ‘Dissertation on the Antiquity of the Batavian Republic,’ for which he received the thanks of the States of Holland, accompanied by a present.

In 1613, he was advanced from his practice as an advocate to the judicial station of Pensionary of Rotterdam, which office was given him for life, the usual tenure having been only at will. In the same year a difference of opinion having arisen between England and the States of Holland, respecting the right of fishing for whales in the Northern seas, Grotius was sent into England for the purpose of effecting an amicable arrangement of the dispute. He there became personally acquainted with Isaac Casaubon, with whom he had previously corresponded. He was favourably noticed by the king during his stay in England, and formed an intimate connexion with several of the most eminent English divines of that day, which he maintained by letters for many years afterwards. In the political object of his embassy he appears to have failed; the subject in dispute was resumed at Rotterdam in 1615, before commissioners of both countries, but with no more favourable result to the Dutch States.

Soon after his return from England, Grotius became deeply involved in the religious animosities which at that time prevailed in Holland. He had adopted the principles of Arminius from Uitenbogard, the instructor of his early youth, and he now zealously maintained the doctrines of the Arminian party in opposition to the tenets held by the followers of Gomar. The questions in dispute related for the most part to predestination and other abstract points of Christian doctrine, the discussion of which by the disciples of Arminius on the one hand, and of Gomar, a professor of Leyden, on the other, had divided the United Provinces into two parties, animated by the most furious hostility towards each other. The public peace being endangered by the violence to which these religious differences were carried, the States of Holland, in 1614, published an edict, drawn up by Grotius, enjoining forbearance and mutual toleration between the contending parties, but denouncing in unqualified terms the doctrines of the Gomarists. The effect of this partial and injudicious edict was to increase the virulence of party spirit; frequent riots ensued, attended with popular demonstrations of an alarming kind. The powerful city of Amsterdam favoured the Gomarists; and hesitated to submit to the edict of 1614. Under these circumstances, the States sent a deputation, of which Grotius was the chief, for the purpose of converting the Town Council of that city to their opinion. Upon this occasion Grotius made a judicious and temperate harangue, which was afterwards translated into Latin, and is published among his works. It was, however, unsuccessful in its result, as the Senate declared that the city of Amsterdam could not adopt the edict without endangering the church, and risking their commercial prosperity. In the mean time popular tumults continued and increased; and in this position of affairs the Grand Pensionary, Barneveldt, proposed to the States of Holland, that the magistrates of the several cities in that province should be authorized to levy soldiers for the purpose of securing the public tranquillity. The representatives of several towns vehemently opposed this proposition, but it was adopted, after a stormy debate; and, August 4, 1617, a proclamation was issued to carry it into execution.

This decree directly induced a train of circumstances, which eventually led to the death of Barneveldt, and the ruin and banishment of Grotius. Prince Maurice of Nassau, who was at that time Governor and Captain-general of the United Provinces, denounced it as an act illegal and unjustifiable in itself, and an invasion of his authority. He influenced the States-General to write to the magistrates of those provinces and cities which had acted under the decree by raising soldiers, commanding them to disband their levies; and upon the refusal of many of them to comply with this requisition, he obtained authority to proceed to the recusant cities, and enforce their obedience. Having executed this commission successfully in the towns of Nimeguen, Overyssel, and Arnheim, Maurice, who on the death of his brother in February, 1618, had assumed the title of Prince of Orange, proceeded to Utrecht, with the same object. The States of Holland had in the mean time sent thither Grotius and Hoogerbertz, the Pensionary of Leyden, for the purpose of opposing the Prince’s commission. They stimulated the magistrates of the city to resist the assumed authority of the States-General, to increase their militia, and to double the guards at the gates. They also brought letters from the States of Holland to the officers of the ordinary garrison, persuading them that it was their duty to obey the States of Utrecht, in opposition to the States-General and the Prince of Orange. Notwithstanding these preparations the Prince entered the city without forcible resistance, and having disbanded the new levies, displaced several magistrates, and arrested some of those who had been most active in their opposition, returned to the Hague. Grotius was now satisfied that all further attempts at opposition would be useless, and prevailed upon the magistrates of Rotterdam at once to dismiss the levies made under the obnoxious decree.

The Prince of Orange and the States-General were highly incensed at the measures taken to excite a forcible opposition at Utrecht; and Barneveldt, Grotius, and Hoogerbertz, were arrested, August 29, 1618, upon the charge of having raised an insurrection at that place, and committed to close custody in the castle of the Hague.

In the ensuing November, the prisoners, having previously undergone repeated examinations, were separately tried before twenty-six commissioners, chosen from the principal nobility and magistracy of the Seven Provinces. Barneveldt was tried first, and was condemned to be beheaded, for various acts of insubordination towards the States; and in particular for having promoted the insurrection at Utrecht. The trial of Grotius followed a few days afterwards. He complains of having been treated then, and during the previous examinations, with great hardship and injustice: he says that he was pressed to answer ensnaring questions directly, when he required time, and that the commissioners refused to read over his examinations to him, after they had written down his answers. He was, however, found guilty, and sentence was passed upon him, May 18, 1619, recapitulating the heads of the charges of which he had been convicted, and condemning him to imprisonment for life, and the confiscation of his estate.

The castle of Louvestein was selected for his place of confinement, a fortress situated near Gorcum, in South Holland, at the point of the island formed at the junction of the Waal and the Meuse. Here he was kept a close prisoner: his father was refused permission to see him, and his wife was only admitted on condition of sharing his imprisonment, being told that if she left the castle she would not be allowed to return. These restrictions were afterwards, however, considerably relaxed: his wife obtained leave to quit the castle twice a week, and Grotius was permitted to borrow books, and to correspond with his friends on all subjects except politics.

It is not for such minds as that of Grotius that “stone walls can make a prison.” During nearly two years of close imprisonment, with no society but that of his wife, who constantly attended him, he employed himself in digesting and applying those stores of learning which he had previously acquired, and study became at once his business and his consolation. “The Muses,” says he, in a letter to Vossius during his confinement, “are a great alleviation of my misfortune. You know that when I was most oppressed by business, they furnished my most delightful recreation; how much more valuable are they to me now, when they constitute the only enjoyment which cannot be taken from me!” During his captivity he occupied much of his time in legal studies, of which other pursuits had for some years caused an intermission, and also in arranging and completing his improvements and additions to Stobæus, which were afterwards published; but his favourite employment appears to have been theology, and especially a laborious and critical examination of the Sermon on the Mount. He also at this time wrote a treatise in the Dutch language on the Truth of the Christian Religion, which a few years afterwards, while at Paris, he enlarged and translated into Latin. In its improved state it became more generally known and popular than any of his works, having been translated, during the seventeenth century, into the English, French, Flemish, German, Persian, Arabic, and Greek languages. This treatise was well worthy of the great attention which it excited: in point of force of argument and clearness of arrangement it will not suffer on a comparison with the works of Paley and other popular modern writers on the same subject; and in temper and candour it is superior to most of them. Grotius says, in the introduction, that he originally wrote it to furnish an occupation to his countrymen during the unemployed leisure of long voyages on commercial adventures; and in the hope that, by thus instructing them in the most intelligible and convincing arguments in favour of Christianity, they might become the means of diffusing its advantages among distant nations. In the first book, he maintains the existence, attributes, and providence of a Supreme Being; in the second, he enumerates the particular arguments in favour of the divine origin of the Christian religion; in which part of the subject his illustration of the internal evidence derived from the superior dignity and excellence of the moral precepts of Christianity is peculiarly admirable. The third division of the treatise contains a critical defence of the authenticity of the books of the New Testament; and the three remaining parts are devoted to a refutation of Paganism, Judaism, and Mahometanism. The perspicuity of the style, and the spirit of candour which pervades the whole treatise, well adapted it to the purpose for which it was intended; and though many modern authors have followed in the same course of reasoning, it may still be read with advantage as an excellent epitome of the arguments for the truth of Christianity.

In the early part of 1621, after nearly two years had been passed by Grotius at Louvestein, the fertile invention of his wife devised the means of his escape. It was his practice to return the books, which he borrowed from his friends, in a large chest, in which his wife sent linen from the castle to be washed at Gorcum. During the first year of his imprisonment the guards invariably examined this chest before it left the castle, but as they continually found nothing but books and dirty linen, they gradually relaxed in their search, until at last it was wholly omitted. Grotius’s wife resolved to turn their negligence to her husband’s advantage. The chest was large enough to contain a man, and she prevailed upon him to try whether he could bear to be shut up for so long a time as would be necessary to convey the chest across the water to Gorcum. The experiment proved the scheme to be practicable, and the first favourable opportunity was seized for carrying it into execution. On the 22nd of March, during the absence of the governor from the castle, Grotius was placed in the chest, and holes having been bored in it by his wife in order to admit air, it was carried down from the castle by two soldiers on a ladder. One of the soldiers, suspecting something from the weight, insisted upon taking it to the governor’s house to be opened; but the governor’s wife, who was probably in the secret, told him she was well assured that the chest contained nothing but books, and ordered him to carry it to the boat. In this manner Grotius crossed the water and arrived safely at a friend’s house in Gorcum. He then passed through the streets in the disguise of a mason, and stepped into a boat which took him to Valvic in Brabant, from whence he afterwards escaped to Antwerp. Upon the first discovery of the trick which had been practised upon him by the wife of Grotius, the governor of Louvestein confined her rigorously; but she was discharged upon presenting a petition to the States-General.

By the advice of various powerful friends in France, Grotius determined to make Paris his city of refuge. He was well received in the French metropolis, both by learned men and politicians, and in the beginning of the following year was presented to the King, who bestowed upon him a pension of 3000 livres. In the year 1622 he published his ‘Apology,’ in which he vindicates his conduct from the particular charges which had formed the subject of the proceedings against him, and argues against the legality of his sentence and the competency of the tribunal by which he was tried. His work excited much attention throughout Europe, and greatly irritated the States-General, who published so violent an edict against it, that the friends of Grotius entertained fears for his personal safety. In order, therefore, to place himself more fully under the protection of the French government, he obtained letters of naturalization from Louis XIII.