In 1340, the Biedma brothers rode south to fight alongside Alfonso XI at the Battle of Salado — the same battle where Pedro Fernández de Castro seized the Moroccan sultan's golden spurs. The two great houses of southern Galicia fought on the same field that day. It would be the last time they stood together.

Juan Rodríguez de Biedma, the third lord, inherited his father's offices and the tenancy of Allariz and Monterrey. He served Pedro I as copero mayor — chief cupbearer, a position of intimate trust. But when the king ordered the execution of Juan Rodríguez's son and heir, Rodrigo Yáñez de Biedma, for having entered what the crown called "royal disservice," the father's loyalty broke. The señor de Biedma switched allegiance to Enrique de Trastámara — and in doing so placed himself on the opposite side of history from Fernando de Castro, the great Petrist loyalist who would hold Galicia for three years after his king's murder.

The Biedma fought against the Castros. When Fernando de Castro held the fortresses of Galicia for Pedro I, Juan Rodríguez de Biedma defended the towers of the Támega, Limia, and Arnoya valleys for the Trastámara pretender. He was besieged in Allariz by Fernando de Castro and forced to flee to Monterrey, where he held out until the end. When Enrique murdered Pedro I with his own hands at Montiel on 23 March 1369, Juan Rodríguez de Biedma was present. He had chosen the winning side.

And he was rewarded for it. Between 1368 and 1369, Enrique II showered the Biedma lord with donations that would define the map of southern Galicia for centuries. In January 1368: Loveira, Entrimo, Araúxo, and Abelenda. In April 1369: Vilanova dos Infantes, Castrelo, and Espinoso. In July 1369: Xinzo de Limia, Gánade, Miño, and Barbantes. And in October, the great final grant, issued at Braganza: "Villa de Rey con todos sus alfoces, e Soto Bermud, con Val de Laza, y el castillo de Santibáñez de Barra, con las tierras de Todea e de Peñafiel."

The irony was bitter. Vilanova dos Infantes, Castrelo, and Espinoso — the three places granted to the Biedma in April 1369 — had previously belonged to the Castros. They had formed part of the dote brought to Pedro Fernández de Castro "el de la Guerra" by his wife Isabel Ponce de León. The lands the greatest Castro lord had held through marriage were stripped from his son's defeated cause and handed to the family that had helped destroy him.

From the marriage of Diego and Elvira came two streams of descendants — and decades of litigation. Juan de Stúñiga, the firstborn, inherited the Biedma and Zúñiga mayorazgos and received the title of Vizconde de Monterrey from Juan II of Castile. But Diego's second marriage, to Constanza Barba de Monsalve, produced a rival line, and the two branches fought over the castle and the lordships for half a century. In 1474, the Reyes Católicos cut through the knot by granting the title of first Conde de Monterrey to Sancho Sánchez de Ulloa, who had married Teresa de Zúñiga y Biedma, the second vizcondesa. The Ulloa name entered the equation, but the underlying patrimony — the Biedma señorío, the Zúñiga titles, the castle overlooking the Támega valley — remained.

The county became one of the great noble states of early modern Galicia. The counts of Monterrey held the Pertiguería Mayor de Santiago — the same military governorship the Castros had wielded in the thirteenth century — and exercised jurisdictional authority over dozens of parishes across southern Ourense. They built the Palacio de los Condes within the walls of the castle, raised the Torre del Homenaje that still dominates the skyline above Verín, and founded a Jesuit college inside the fortress walls where their sons were educated.

But the most extraordinary Monterrey was Gaspar de Zúñiga y Acevedo, the fifth count, born inside the castle in 1560. Born señor de Biedma, Ulloa, and de la Casa de la Ribera, and pertiguero mayor de Santiago, Gaspar studied under the Jesuits his grandfather had installed in the fortress, then entered the service of Philip II. He led the Galician militia during the Portuguese campaign, defended La Coruña against the English corsair Francis Drake in 1589, and in 1595 was named Viceroy of New Spain. On 20 September 1596, Diego de Montemayor founded a city in the northern reaches of the viceroyalty and named it after his sovereign's representative: Nuestra Señora de Monterrey. Monterrey, Mexico — the great industrial capital of northern Mexico — carries the name of a castle in Ourense. When Sebastián Vizcaíno explored the coast of California in 1602, he named the finest bay he found in honour of the same viceroy: Monterey Bay. From Galicia to Mexico to California — the name of a Navarrese-Galician frontier family inscribed on the map of two continents.

Gaspar died in Lima in 1606, having served as viceroy of Peru after New Spain. His debts were so great that the Royal Audiencia had to pay for his funeral. His body was returned to Spain and buried in the Jesuit church inside the castle of Monterrey — the same fortress where he had been born.

The Casa de Zúñiga-Biedma bore two sets of arms, each with its own story. The Zúñiga shield — argent, a bend sable, brochant over all a chain of eight links or in orle — was among the most recognisable armorial devices in Spain. The Biedma shield — or, a pale gules between eight calderas sable, four to each side — signalled the military heritage of a frontier house charged with defending the southern approaches to Galicia.

The Zúñiga arms changed twice. The original device was a golden band on red. After the Battle of Las Navas de Tolosa in 1212, when Navarrese knights broke through the chain-linked human wall of the Almohad caliph's Black Guard, the Zúñiga added a gold chain of eight links in border — the same device that entered the arms of the Kingdom of Navarra itself. In 1270, Diego López de Stúñiga changed the colours again, to silver, black, and gold, in mourning for the deaths of Saint Louis IX of France and Theobald II of Navarra during the Eighth Crusade. The arms remained unchanged from that date. The black band across a silver field, enclosed by a chain of gold, was carried from Navarra to Castile, from Castile to Galicia, from Galicia to the Americas.

The Biedma calderas — the heraldic cooking pots that denoted the right to maintain armed retainers and feed a war host — marked the family as ricoshombres, magnates of the first rank. The two shields united in 1406. When they appear together on the facade of a church in Cartelle, in the province of Ourense, they still speak across seven centuries.