Two cannons bearing the coat of arms of the Counts de Gavre will highlight Bonhams' Antique Arms & Armour auction on July 31 in London.

The Counts de Gavre rose to prominence under the crusader kings of Jerusalem and Cyprus in the 11th century

Dating to the 17th century or later, the cannons are valued at a combined £18,000-22,000 ($27,000-33,000) and will sell in a single lot.

As well as the coat of arms, the cannons are also inscribed with "Gavre au chaplet", which was the battle-cry of the troops raised by the Counts de Gavre.

The family originates from Flanders, Belgium and became prominent while serving under the crusader kings of Jerusalem and Cyprus in the 11th century. They were also prominent in Spain and the Austrian Netherlands.

The first member of the family to be initiated into the highly-respected Order of the Golden Fleece was Jacques de Gavre, who was councillor to Emperor Charles V during the time of the Holy Roman Empire.

As a result, his family was awarded the title of Princes of the Holy Roman Empire by Charles VI in 1736.

Elsewhere, a rare Viking sword of Peterson Type H from the 9th century will sell with a £8,000-12,000 ($12,000-18,000) estimate.

The sword remains in excavated condition. Its pommel still bears the remains of its twisted silver wire decoration.

Also featuring in the sale is an 1805 officer's sword that was commissioned by King William IV, the Sailor Prince.

See our militaria for sale, which includes a fantastic signed letter from British naval hero Lord Nelson.