One-ruble coin, 1825 Obverse side

One of the rarest and most famous coins in the history of Russian
monetary circulation is the so-called ‘Constantine ruble’, a valuable
testament to one of the most dramatic and mysterious moments in
Russian history.
After the sudden death of the childless Emperor Alexander I in
Taganrog, on 19 November 1825, the throne was to pass to his brother,
Grand Duke Constantine Pavlovich. However, in 1823, the emperor had
signed a secret manifesto on the abdication of Constantine from the
throne in favour of his younger brother Nicholas Pavlovich. Before the
manifesto was announced, Nicholas swore an oath to Constantine, which introduced ambiguity into the interpretation of the document,
and the Imperial Russian Guard continued to swear allegiance to
Constantine. The interregnum lasted two weeks and ended with the
Decembrist Revolt. At the St Petersburg Mint, precisely during those
troubled days, on the orders of Finance Minister Egor Cankrin work
began on the new emperor’s coin. Medallist J. J. Reichel prepared its
sketch, dies were cut, and trial coins with a portrait of Constantine
were minted. Following the uprising and the reign of Emperor Nicholas
I, all documents, tools, and trial coins were secured for many years
in the Ministry of Finance’s secret archive. Only in 1879 did these
artefacts see the light of day, and the rare trial specimens were
personally distributed by Emperor Alexander II to nobles close to him.

Constantine’s bust, facing right.
Circular legend: Б. М. КОНСТАНТИНЪ I. ИМП. И САМ. ВСЕРОСС. (BY THE
GRACE OF GOD, CONSTANTINE, EMPEROR AND SOLE RULER OF ALL
RUSSIA). At bottom, year: 1825.