"The pearl of the Carpathians" - as it is called today, Sinaia is a settlement inhabited since the Neolithic Age, with a name having as its starting point a monastery derived from the name of the Holy Mountain of Sinai. Foundation of Mihail Cantacuzino, the small sanctuary sanctified on August 15, 1695, often provided shelter to the pilgrims or merchants who ventured to cross the wild "road of Prahova", the commercial route whose existence was attested since the 12th century.

The deserted area of ​​the Prahova Valley, where the city of Sinaia is today, was uninhabited in the 17th century, the first inhabitants settling in the virgin forest here, at the foot of the Bucegi Mountains, were the monks of the Sinaia monastery, founded between 1690- 1695 by the great Mihai Cantacuzino, as well as some scouts who were in charge of guarding the monastery. The city took the name of the monastery, and the monastery was named like this after the trip of the ruler to Saint Catherine's Monastery in the Sinai Peninsula.

At the beginning of the nineteenth century, the entire Prahova Valley was organized as a single commune, called "Podul Neagului", comprising the entire valley, from Predeal to Posada. In 1864 Posada and Podul Neagului were annexed to Comarnic.

On August 5, 1866 Prince Carol I of Romania arrived to the Sinaia Monastery, situated at that time in Podul Neagului commune. He was involved in the organization of the region, and in 1874 the small settlements that remained outside Comarnic commune were named Sinaia. A report dated from December 1, 1874, confirms that the residence of Podul Neagului commune was moved in Sinaia, which changed its name in that year (from that of the Sinaia Monastery, whose name also comes from that of the Mountain Sinai).

On May 9, 1880, Sinaia acquired the status of an urban commune and included the small towns of Izvor, Furnica and Poiana Tapului. The town of Sinaia was thus detached from the commune of Podul Neagului, which relocated its residence back in Comarnic. In 1884, Predeal, Azuga, Busteni and Poiana Tapului separated from Sinaia, forming the Predeal commune, while the commune of Sinaia remained with the towns Izvoru and Furnica. During the same period, the royal family of Romania settled in Sinaia in summer, building the beautifyl Peles Castle. At the end of the 19th century, the commune had a population of 2210 inhabitants, a mixed school frequented in 1899 by 103 students, hotels, the railway station Ploiesti-Brasov, the hydrotherapy clinic and the Sinaia monastery.

Also at that time, the city began to become an industrialized one, with a timber factory owned by the industrialists Popovici and Costinescu. Also, in January 1892, an iron factory was opened with only 45 employees. From an administrative point of view, the commune was the residence of Pelesul Plateau in Prahova county.