They were encouraged by the dissension which resulted when Constantine refused the throne, and occupied Senate Square shortly after the brother of Alexander I took power, only to be fired upon by loyal soldiers.  
A year after it, a commission led by Mikhail Speransky came together to consider legal reforms.  When five of its leaders were supposed to be hanged, three of the ropes broke, leading Ryleyev to quip that a country where they don't even know how to hang you is unhappy indeed.  The factions led by Nikita Muraviev hoped to bring about a constitutional monarchy, while the one led by Pavel Pestel aimed for a republic.  They were encouraged by the dissension which resulted when Constantine refused the throne, and occupied Senate Square shortly after the brother of Alexander I took power, only to be fired upon by loyal soldiers.  FTP, name this uprising of 1825 which opposed the autocratic rule of Nicholas I, whose name refers to the winter month in which it took place.
A year after it, a commission led by Mikhail Speransky came together to consider legal reforms.  
the Decembrist Uprising (accept equivalents like the Decembrist Revolt, etc.)