On what date was the warning letter to Lord Monteagle delivered before the Gunpowder Plot?

The warning letter to Lord Monteagle was delivered on 26 October 1605, shortly before the Gunpowder Plot was uncovered.

The anonymous letter advised Monteagle not to attend Parliament and urged him to withdraw to the countryside. Monteagle passed it to Robert Cecil, the king’s principal minister, who helped arrange searches of the parliamentary buildings.

The letter did not immediately identify every conspirator, and historians have debated who wrote it. Francis Tresham is often named as the likely author, although the evidence is not conclusive. The warning’s wording was sufficiently clear to prompt official suspicion.

The letter is important because it connected the planned parliamentary explosion with a specific warning before the conspirators could act. Its delivery helped turn a secret Catholic conspiracy into a government investigation.