Pope Benedict XVI's shock resignation in February meant that Vatican City had to issue Vacant See stamps in March, as it has done on five previous occasions.

Inscribed 'Sede Vacante MMXIII', the four values of 70c, 85c, €2 and €2.50 all illustrate the Arms of the Apostolic Camera, including the crossed keys of St Peter, in four different colours.

Since the 1950s, the standard practice has been that Vacant See stamps are designed shortly after a new Pope accedes to the Pontificate, and the designs remain on file until he vacates the post (usually on his death). They are then printed as necessary.

Such stamps were issued following the deaths of Popes in 1958, 1963, 1978 (twice in quick succession) and 2005. In each previous case they comprised a set of three.

In the stamp age, the See has been vacant for no longer than 20 days, although of course it can take longer for replacement stamps commemorating the enthronement of a new Pope to appear.