On May 9, 1913 (April 26, old style) in St. Petersburg, the so-called Petersburg Protocol, by which Bulgaria agreed to cede to Romania the city of Silistra along with a three-kilometer zone around it.
This territorial concession was the result of the mediation of the Great Powers in the dispute between the two countries after the First Balkan War.
Romania demanded territorial compensation from Bulgaria for Bulgarian territorial expansion in Thrace and Macedonia, threatening military intervention.
The decision was made during a conference of ambassadors of the Great Powers (Russia, Austria-Hungary, Germany, France, Great Britain and Italy) in the Russian capital.
In addition to the surrender of Silistra, Bulgaria committed not to build fortifications along the new border and to grant religious and school autonomy to the Aromanians in Macedonia.
Despite this concession, Romania was not satisfied and later joined the The Inter-Allied War, which led to the loss of all of Southern Dobrudja according to the Treaty of Bucharest of July 1913.
On the same day - May 9 - but four years later, in 1917, one of the greatest victories of the Bulgarian Army during the First World War, often called the “May Battle“, took place.
It was part of the Entente's large-scale spring offensive on the Macedonian Front, which aimed at a decisive breakthrough and removing Bulgaria from the war.
Against the positions of the 11th German-Bulgarian Army, significantly superior Entente forces faced them - French colonial divisions, Italian units (35th Infantry Division) and Russian troops (2nd and 4th Special Brigades). They have about 69 battalions, over 500 machine guns and over 400 cannons.
Against them are Bulgarian units of the 8th Tundzha, 302nd (mixed) and units of the 9th Pleven Division, supported by German batteries. They defend a front of about 23 km with fewer resources: about 40 battalions and 122 cannons.
The attack was preceded by 4 days of massive artillery preparation. On May 5 alone, the Allies fired over 15,000 shells at the Bulgarian positions.
On May 9 at 6:30 a.m., three successive waves of attack began. The main blow was aimed at the strategic heights 1,050 and 1,020.
The Bulgarian artillery and infantry managed to repel all attempts at a breakthrough. The Russian brigades suffered catastrophic losses (the 2nd Special Brigade alone lost nearly 1,000 men), which turned May 9 into a “black day” for the Russian army in Macedonia.
The Entente forces lost over 5,400 men (killed and wounded), while the Bulgarian losses were significantly smaller – about 1,600 people.
The failure of the offensive forced the Entente command to cease active operations in this sector until the fall of 1918.
During these May battles, on May 26, the legendary Colonel Boris Drangov, commander of the 9th Plovdiv Infantry Regiment, was seriously wounded and later died.