Soon after Paul was murdered in a palace coup Brenna, renowned for fraud and embezzlement barely tolerated by his late patron,[2] retired and left Russia for an uneventful life in Saxony.

Brenna never reached the level of his better known contemporaries Giacomo Quarenghi, Charles Cameron and Vasili Bazhenov and was soon surpassed by his own trainee Carlo Rossi.

[3] Nevertheless, historians Igor Grabar,[4] Nikolay Lanceray[4] and Dmitry Shvidkovsky[5] praised him for sincere and unrestricted naturalism of his graphic work and considered him to be the watershed between the Age of Enlightenment and Romanticism in Russian architecture.

Karl Enrico Brenno (Brennus) carved elaborate tombs in Denmark and Hamburg, but was better known for his marbling artwork at Fredensborg, Christiansborg and Klausholm palaces.

[8] Brenna himself did not have luck in tangible architecture; instead, commissioned by Lodovico Mirri[9][10] under auspices of Pope Clement XIII, he surveyed the relics of Rome together with Franciszek Smuglewicz.

[19] Aspiring Brenna was caught in the middle of "battle of the palaces", an expensive ideological contest between Catherine and Paul "hidden from the uninitiated but known to the court".

Paul's trusted barber Count Ivan Kutaisov, another Pavlovsk landlord, became Brenna's first private customer; he commissioned a summer dacha in "medieval style".

[28] Paul and Maria's private suites were redesigned in austere styling with inexpensive materials, in contrast with lavishly decorated public halls.

In 1796 Paul launched construction of a military base for his trusted Gatchina troops; the project, led by Brenna, also employed Bazhenov, Ivan Starov, Andreyan Zakharov and Nikolay Lvov, architect of the Priory Palace.

[18] Brenna's major additions to Pavlovsk Palace materialized after Paul's ascension to the throne; the architect prepared drafts over the winter of 1796-1797 and work commenced in spring of 1797.

[37][38] According to Dmitry Shvidkovsky, the architect and the emperor shared the Romantic vision of art; this emotional bond explains Brenna's survival at the court of an irrational tsar.

It took two months to demolish the old structures on site; groundbreaking was celebrated in February 1797[41][42] but actual work commenced in earnest on March 11, exactly four years before Paul's murder.

[43] Initial cost budget reached 1.5 million roubles in gold, not including interior finishes[44] Paul shut down Catherine's projects in Tsarskoye Selo and placed the redundant workforce at Brenna's disposal.

[45] He wanted to see the castle externally complete by the end of 1797, so work on site, employing up to 6,000 men, continued day at night while all other residents of Saint Petersburg were ordered to sleep after dusk.

Paul agreed and allowed Brenna unchecked access to state finances;[48] in the end, total cost of the Castle reached six million roubles in gold.

[51] Moisture inside the ballroom was so high that candlelight could not break through the wall of fog; Paul and Maria left and returned to the castle only on February 1, 1801.

[52] Despite all setbacks, four-year construction period was unprecedented for a large palace; contemporaries and modern historians agree that Brenna proved himself a capable project manager.

[37][53] In addition to Saint Michael's Castle, he was still responsible for works performed at Gatchina, Pavlovsk, Petergof and Tsarskoye Selo;[54] he managed hundreds of suppliers and contractors, hired European artists, squeezed discounts out of merchants, arranged geological expedition scouting for proper granite deposits.

[53] Unlike Cameron, Brenna never hesitated to assign less-than-competent artists to "fill the void" and make the schedule; he focused on the whole picture and did not seek perfection in detail.

Paul himself was aware of Brenna's misconduct and was credited with a pun, in French language: "Voila l'architecte qui vole" (voler can be interpreted as soar as well as steal).

Murder of Paul (March 11, 1801) and ascension of Alexander I of Russia spelled end of Brenna's career; he was not even invited to decorate the funeral ceremonies.

[57] The family council decided to leave Russia for Saxony; other Italians (Concensio Albani, Antonio Rusca, Giuseppe Sarti) followed, for different reasons.

He sold his art treasures and in January 1802 tended his resignation to Maria Fyodorovna, the latter granted him annual pension of 3525 roubles (half of his salary).

[3] Lanceray noted Brenna's weakness in floorplan designs, labeling them "helpless and primitive",[3] and praised him for nearly perfect facades of Saint Michael's Castle.

[3] Dmitry Shvidkovsky elaborated on the "watershed" theory, linking Brenna's art to his Roman studies: "No partisan of strict Antiquity like Cameron, he was able to combine the solemn image of Imperial Rome with heightened pre-Romantic emotionalism.