The Twelfth, Battle of the Boyne 2035

What is commemorated
12 July marks the Battle of the Boyne of 1690, at which William of Orange defeated the deposed James II near Drogheda. It was the turning point in securing the Protestant succession in Britain and Ireland, though the war in Ireland ran on for another year, to Aughrim and the Treaty of Limerick. The anniversary has been kept in Ulster ever since.

The date puzzle
The battle was fought on 1 July under the Julian calendar then in use. A straight conversion would give 11 July, but the anniversary had already merged with that of the Battle of Aughrim, fought on 12 July 1691 and at the time reckoned the more decisive victory. The eleven-day adjustment made when Britain adopted the Gregorian calendar in 1752 fixed the commemoration on 12 July, where it has stayed.

Where it is a bank holiday
The Twelfth is a bank holiday in Northern Ireland only, proclaimed each year by the Secretary of State. It is not a holiday in England, Wales or Scotland.

Parades and bonfires
The Orange Order holds parades in towns across Northern Ireland, with lodges, banners and marching bands. Large bonfires are lit on the evening of the eleventh. The day is the high point of what is locally called the marching season, and it remains contested: some communities experience the parades as celebration and others as provocation.

Substitute days
As a fixed date it moves when it falls at the weekend: if 12 July is a Sunday the holiday is taken on the 13th, and if it is a Saturday on the following Monday, the 14th. It is one day either way, not two.

UK bank holidays 2035