[5] Beyond this, though, his early military career is a mystery: one source identified him as a colonel of the Légion des Volontaires de Luxembourg on 1 October 1785.

On 15 October, Henri François Delaborde and his division advanced south from Elizondo across the Puerto de Belate (Velate Pass), driving Antonio Filanghieri's 2,000 Spanish troops from Lantz.

Joined there by Castelverd's column, Delaborde moved east to the royal foundry at Eugi where the French defeated 4,000 Spaniards on the 16th.

After another clash on the 17th, the beaten force fell back farther east and joined Pedro Téllez-Girón, 9th Duke of Osuna and his troops near Burguete.

[9] The Rhine Campaign of 1796 was ending badly for the French when the Army of Sambre-et-Meuse under Jean-Baptiste Jourdan retreated behind the Lahn River on 9 September.

With their strategy in ruins, the French Directory belatedly awoke to the reality that the unemployed Army of the North might provide reinforcements.

MacDonald was held back to defend Düsseldorf but Castelverd's troops were inserted into the defenses on the lower Lahn under the direction of the right wing commander François Séverin Marceau-Desgraviers.

Despite the odds, the division of André Poncet held its ground stubbornly through eight hours of combat, retaining Limburg but yielding a small bridgehead at Diez.

Marceau believed the situation was well in hand and planned to retake Diez the next morning with four battalions of infantry and eight squadrons of cavalry.

His instructions from Marceau were to, "defend the two crossings with the utmost obstinacy, and you will not dream of retreating until after being completely driven in, or after receiving an order to do so."

[12] That evening Adjutant-General Nicolas Léonard Beker arrived at Castelverd's headquarters with the news that the Diez crossing had fallen to the Austrians but that French troops still sealed off the bridgehead.

Fortunately for Jourdan, Marceau and Bernadotte capably held off the Austrian advance guards long enough for the French left wing to barely get away.

On 19 September, as the last French columns were still filing through Altenkirchen, Jourdan ordered Marceau to hold on a little longer with Poncet's division.

[14] Afterward, MacDonald asked Castelverd why he retreated when the enemy wasn't pressing him and giving his commander such short notice of his action.