I think that GD Konstantin don't have his own tread. I know that there is a tread on Anna Feodorovna and that there is some information on GD Konstantin, but why not a tread of his own.
So, here is a bio on GD Konstantin:
Constantine Pavlovich Romanov (27 April, 1779–27 June, 1831), Grand Duke and Tsarevich of Russia, was prepared by his grandmother, Catherine the Great, to become an emperor of the would-be restored Byzantine Empire. Although he was never crowned, he is sometimes listed among the Russian emperors as Constantine I. He was mainly known for his abdication from the throne in 1825, which led to the Decembrist rebellion later that year. In his capacity of the first Viceroy of the Congress Kingdom of Poland, he is remembered as a ruthless ruler.
Constantine was born at Tsarskoye Selo on 27 April 1779. Of the sons born to the Tsar Paul Petrovich and his wife Maria Feodorovna, the Princess of Württemberg, none more closely resembled his father in bodily and mental characteristics than did the second, Constantine Pavlovich.
The direction of the boy's upbringing was entirely in the hands of his grandmother, the Empress Catherine II. As in the case of her eldest grandson (afterwards the Emperor Alexander I), she regulated every detail of his physical and mental education; but in accordance with her usual custom she left the carrying out of her views to the men who were in her confidence. Count Nicolai Ivanovich Saltykov was supposed to be the actual tutor, but he too in his turn transferred the burden to another, only interfering personally on quite exceptional occasions, and exercised neither a positive nor a negative influence upon the character of the exceedingly passionate, restless and headstrong boy. The only person who really took him in hand was Cesar La Harpe, who was tutor-in-chief from 1783 to May 1795 and educated both the empress's grandsons.
Like Alexander, Constantine was married by Catherine, when he was not yet seventeen years of age (26 February 1796), a raw and immature boy, and he made his wife, Juliane of Saxe-Coburg-Saalfeld (Queen Victoria's aunt), intensely miserable. After the first separation in the year 1799, she went back permanently to her German home in 1801, the victim of a frivolous intrigue, in the guilt of which she was herself involved. An attempt made by Constantine in 1814 to win her back to his hearth and home broke down on her firm opposition.
During the time of this tragic marriage Constantine's first campaign took place under the leadership of the great Suvorov. The battle of Bassignano was lost by Constantine's fault, but at Novi he distinguished himself by such personal bravery that the Emperor Paul bestowed on him the title of Tsarevich, which according to the fundamental law of the constitution belonged only to the heir to the throne. Though it cannot be proved that this action of the tsar denoted any far-reaching plan, it yet shows that Paul already distrusted the Grand Duke Alexander.
Constantine never tried to secure the throne. After his father's death he led a wild and disorderly bachelor life. He abstained from politics, but remained faithful to his military inclinations, without manifesting anything more than a preference for the externalities of the service. In command of the Guards during the campaign of 1805, he had a share of the responsibility for the unfortunate turn which events took at the battle of Austerlitz; while in 1807 neither his skill nor his fortune in war showed any improvement.
After the peace of Tilsit he became an ardent admirer of the great Corsican and an upholder of the Russo-French alliance. It was on this account that in political questions he did not enjoy the confidence of his imperial brother. To the latter the French alliance had always been merely a means to end, and after he had satisfied himself at Erfurt, and later during the Franco-Austrian War of 1809, that Napoleon likewise regarded his relation to Russia only from the point of view political advantage, he became convinced that the alliance must transform itself into a battle of life and death. Constantine did not hold this view; even in 1812, after the fall of Moscow, he pressed for a speedy conclusion of peace with Napoleon, and, like field marshal Kutuzov, he too opposed the policy, which carried the war across the Russian frontier to victorious conclusion upon French soil.
During the campaign he was a boon companion of every commanding officer. Barclay de Tolly was twice obliged to send him away from the army. His share in the battles in Germany and France was insignificant. At Dresden, on the 26th of August, his military knowledge failed him at the decisive moment, but at La Fère-Champenoise distinguished himself by personal bravery. In Paris the Grand Duke excited public ridicule by the manifestation of his petty military fads. His first visit was to the stables, and it was said that he had been marching and drilling even in his private rooms.