Siemens Velaro RUS Sapsan, Moscow, St. Petersburg

Explanation of "Sankt-" by the appreciation of Dutch culture by Peter the Great is one of common misconceptions: "Saint-" in Dutch is "Sint". The sample which czar Peter followed sounds in the names of another European cities: Sankt Goar in Germany, Sankt Michael in Austria and some others, of which the closest to Sankt Petersburg was Sankt Michel in rival Swedish Empire (now Mikkeli in Finland). "Sankt-" in these toponyms is merely a Germanized form of Latin: Sanctus.
A 14-15-letter long name, composed of the three roots proved too cumbersome, and a lot of shortened versions appeared in habitual use. The first General Governor of the city Menshikov is maybe also the author of the first nickname of Petersburg which he called Петри (Petri). It took some years until the known Russian spelling of this name finally settled. In 1740s Mikhail Lomonosov uses a derivative of Greek: Πετροπόλης (Petropolis, Петрополис) in a russified form Petropol’ (Петрополь). A combo Piterpol (Питерпол) also appears at this time. Anyway, eventually the usage of prefix "Sankt-" ceased except for the formal official documents, where a 3-letter abbreviation "СПб" (SPb) was very widely used as well.
In the 1830s Alexander Pushkin translated the 'foreign' city name of 'Saint Petersburg' to the more Russian Petrograd in one of his poems. However, it was only on 31st August 1914, after the war with Germany had began, did tzar Nicholas II rename the capital to Petrograd. Since the prefix 'Saint' was omitted, this act also changed the eponym and the 'patron' of the city, from Apostle Peter to Peter the Great, its founder.
After the October Revolution, and until the city was renamed Leningrad in January 1924, the name Красный Петроград (Red Petrograd) was often used in newspapers and other prints.