On August 15-16, 1914, during World War I, the Battle of Cer began. From the article:
"The Battle of Cer, also popularly known as Battle of the Jadar River, was fought in August 1914 between Serbia and Austria-Hungary during the early stages of the First World War. This battle took place around the Cer Mountain, Sabac town, and some other surrounding villages. The battle was part of the very first Austro-Hungarian invasion of Serbia.
The Battle Begins
On the night of August 15th, 1914, the battle began when some elements of the Serbian First Combined Division encountered the Austro-Hungarian outposts that had been established on the slopes of Cer Mountain. The clashes that followed escalated into a battle that resulted to over 3,000 casualties with 15,000 people being wounded.
Background of the War
On June 28th, 1914, Gavrilo Princip, a student of a Bosnian Serb, assassinated Archduke Franz Ferdinand of Austria. This assassination precipitated the July Crisis that led Austria-Hungary to issue an ultimatum to Serbia on July 23rd. This was on the suspicion that the assassination was an earlier plot in Belgrade.
This ultimatum was intentionally unacceptable to the Serbian government and so it was rejected. On July 28th, war was officially declared and Belgrade was shelled the following day. This marked the beginning of World War One.
From July 29th to August 11th, the Austro-Hungarian army launched artillery attacks in the northern and northwestern part of Serbia. They managed to exploit bombardments by constructing pontoon bridges across the Drina and Sana Rivers. The Serbians were aware that it was impossible for their army to line the entire Austro-Serbian border that extended more than 340 miles.
Therefore, Putnik ordered that the Serbian army fall back as he regrouped his forces in Sumadija. From Samadija, the Serbian army could easily move either west or north. More and more vigorous artillery bombardments were continuously subjected to Smederevo, Belgrade and Veliko Gradiste. This and other few failed attempts to cross the Danube resulted in heavy Austro-Hungarian losses.
On August 12th, Austro-Hungarian troops managed to enter Serbia via Loznica town. By August 14th, over a front of about 100 miles, the Austro-Hungarians had already crossed the rivers and converged on Valjevo. The other part of Austro-Hungarian Amy moved towards Belgrade, where they faced the Serbian Armies. On 15th August, Putnik ordered his forces to launch a counterattack.
The Battle Begins
A few hours before midnight on August 15th, fighting erupted on the slopes on Cer Mountain. The Austro-Hungarian positions were lightly held and their soldiers were driven back away from this mountain. By midnight, fierce clashes had developed between the two armies and the Serbs were underway and chaos ensued in the darkness. By morning on August 16th, the Serbians had seized the Divaca Range and also dislodged the Austro-Hungarians from their positions.
On August 17th, the Serbian army tried to retake Sabac, but their efforts failed. On August 18th, the Austro-Hungarians launched another attack, but this failed. The next day, the Serbs finally crushed the Austro-Hungarians and by noon on that day, they had conquered Rasulijaca.
Before midday, Velika Glava village fell to the Serbs and by the late afternoon, Rajin Grob was also retaken. By this time, the Austro-Hungarians started retreating quickly; their will and cohesion apparently shattered. By August 20th, the Austro-Hungarian armies were fleeing across Drina River. Before long, the Serbs reached the banks of the River Sana, bringing the first Austro-Hungarian invasion of Serbia to an end.
Casualties of Battle
Both sides suffered heavy casualties. The Austro-Hungarians suffered 37,000 casualties, of which 7,000 were fatalities. About 3,000 Serbian soldiers were also killed and 15,000 wounded in the Battle of Cer."