the new royal castle of
Montgomery, he laid siege to it in 1228. Hubert de Burgh, then
castellan of Montgomery, could only save his castle by summoning the
levies of the kingdom. At their head Hubert went in person to hold the
field against Llewelyn, taking the king with him. The Welsh withdrew as
usual before a regular army, and Hubert and the king, late in
September, marched a few miles westwards of Montgomery to the vale of
Kerry, where they erected a castle. But Llewelyn soon made the English
position in Kerry untenable. Many of the English lords were secretly in
league with him, and the army suffered severely from lack of food. In
the fighting that ensued the Welsh got the better of the English,
taking prisoner William de Braose, the heir of Builth, and one of the
greatest of the marcher lords. At last king and justiciar were glad to
agree to demolish the new castle on receiving from Llewelyn the
expenses involved in the task. The dismantled ruin was called "Hubert's
folly". "And then," boasts the Welsh chronicler, "the king returned to
England with shame."

In 1230 Llewelyn inflicted another slight upon his overlord. William de
Braose long remained the Welsh prince's captive, and only purchased his
liberty by agreeing to wed his daughter to Llewelyn's son, and
surrendering Builth as her marriage portion. The captive had employed
his leisure in winning the love of Llewelyn's wife, Joan, Henry's
half-sister. At Easter, Llewelyn took a drastic revenge on the
adulterer. He seized William in his own castle at Builth, and on May 2
hanged him on a tree in open day in the presence of 900 witnesses.
Finding that neither the king nor the marchers moved a finger to avenge
the outrage done to sister and comrade, Llewelyn took the aggressive in
regions which had hitherto been comparatively exempt from his assaults.
In 1231 he laid his heavy hand on all South Wales, burning down
churches full of women, as the English believed, and signalling out for
special attack the marshal's lands in Gwent and Pembroke. Once more the
king penetrated with his barons into Mid Wales, while the pope and
archbishop excommunicated Llewelyn and put his lands under interdict.
Yet neither temporal nor spiritual arms were of avail against the
Welshman. Henry's only exploit in this, his second Welsh campaign, was
to rebuild Maud's Castle in stone. He withdrew, and in December agreed
to conclude a three years' truce, and procure Llewelyn's absolution.