The taking of Arras furnishing an occasion to compliment the King, Grotius went to St. Germains in the beginning of November, 1640.  He expressed to his Majesty the joy he received by his happy return, his good health, and the conquest of such a considerable town as the capital of the Artois:  he added his sincere wishes for the further increase of the prosperity of France, and the happy delivery of the Queen, who was then with child of the Duke of Anjou, afterwards Duke of Orleans.  The King seemed to be pleased with this compliment, and mentioned some of the difficulties which attended the siege of Arras.  Grotius afterwards spoke to the King of Marshal Horn:  he told his Majesty that he had received letters from him, assuring that the Duke of Bavaria consented to his being exchanged for John de Vert.  The Ambassador added, that the Duke of Weymar always desired the exchange:  and that, if his Majesty would do Sweden this pleasure, John de Vert might be sent to Benfeld, and Marshal Horn to Landau, and both be afterwards set at liberty at Basil.  The King answered, that he would think seriously of it.

In fact, Chavigny came soon after to see Grotius, and told him that the King, after reflecting on the proposals he had made to him concerning Marshal Horn’s release, had resolved to send John de Vert to Nancy as soon as the troops were in winter quarters, that he might be sent back with a more considerable escort; that he consented the Marshal should be exchanged for John de Vert, on condition, however, that the treaty between France and Sweden should be renewed.  Chavigny added, that the King, having learnt that Grotius complained of the Chancellor Seguier for denying him the honours due to an Ambassador, had signified his intentions, that he should be treated as the other Ambassadors of crowned heads.  Grotius having made a visit a little before[395] to the Chancellor of France, he had neither advanced to meet him, according to custom, nor given him the place that was due to him, nor re-conducted him on coming away.  The Ambassador complaining of it, Count Brulon came and told him in presence of the Chancellor’s servants, that if any offence had been given him, it proceeded from inattention, and not from design; for the King would have him treated with the same honours as other Ambassadors of Kings.  Grotius replied, that he expected to receive the same treatment as the English Ambassador:  on which Count Brulon said, France gave to each power the honour due to its rank.

The exchange, however, was not executed.  Grotius made a journey to Rheims, where the King was, to speak to him of it[396].  The King gave him the most positive promises, and engaged to give John de Vert his liberty, if the Duke of Bavaria sent Marshal Horn to Landau.  Grotius wrote to the Court of Bavaria; John de Vert was conducted to Selesdad:  and at last the exchange was made at Strasbourg.  Grotius wrote a letter[397] of compliment on it to the Marshal, and desired him to come and lodge with him, if he purposed to pass through Paris in his way to Sweden.