Page "Robert the Bruce" Paragraph 19

On 11 June 1304, with both of them having witnessed the heroic efforts of their countrymen during King Edward's siege of Stirling Castle, Bruce and William Lamberton made a pact that bound them, each to the other, in “ friendship and alliance against all men .” If one should break the secret pact, he would forfeit to the other the sum of ten thousand pounds.

The pact is often interpreted as a sign of their deep patriotism despite both having already surrendered to the English.