Battle of Cer The Battle of Cer ( ; ; ) , also known as the Battle of the Jadar River ( Јадарска битка / " Jadarska bitka " , " Schlacht von Jadar " , " Jadar csata " ) , was fought between Austria - Hungary and Serbia in August 1914 during the early stages of the Serbian Campaign of the First World War . It took place around Cer Mountain and several surrounding villages , as well as the town of Šabac . The battle , part of the first Austro - Hungarian invasion of Serbia , began on the night of 15 August when elements of the Serbian 1st Combined Division encountered Austro - Hungarian outposts that had been established on the slopes of Cer Mountain earlier in the invasion . The clashes that followed escalated into a battle for control over several towns and villages near the mountain , especially Šabac . On 19 August , the morale of the Austro - Hungarians collapsed and thousands of soldiers retreated back into Austria - Hungary , many of them drowning in the Drina River as they fled in panic . On 24 August the Serbs re - entered Šabac , marking the end of the battle . Serbian casualties after nearly ten days of fighting were 3 , 000 – 5 , 000 killed and 15 , 000 wounded . Those of the Austro - Hungarians were significantly higher , with 6 , 000 – 10 , 000 soldiers killed , 30 , 000 wounded and 4 , 500 taken as prisoners of war . The Serb victory over the Austro - Hungarians marked the first Allied victory over the Central Powers in the First World War , and the first aerial dogfight of the war took place during the battle . Background . On 28 June 1914 , Bosnian Serb student Gavrilo Princip assassinated Archduke Franz Ferdinand of Austria in Sarajevo . The assassination precipitated the July Crisis , which led Austria - Hungary to issue an ultimatum to Serbia on 23 July on suspicion that the assassination had been planned in Belgrade . The Austro - Hungarian government made the ultimatum intentionally unacceptable to Serbia , and it was indeed rejected . War was declared on 28 July and Belgrade was shelled the next day , marking the beginning of the First World War . Fighting in Eastern Europe began with the first Austro - Hungarian invasion of Serbia in early August 1914 . The number of Austro - Hungarian troops assigned to such an invasion was far smaller than the 308 , 000 - strong force intended when war was declared . This was because a large portion of the Austro - Hungarian 2nd Army had moved to the Russian Front , reducing the number of troops involved in the initial stages of the invasion to approximately 200 , 000 . Forty percent of this force was composed of South Slavs living within Austro - Hungarian borders . On the other hand , the Serbs could muster some 450 , 000 men to oppose the Austro - Hungarians upon full mobilization . The main elements to face the Austro - Hungarians were the 1st , 2nd , 3rd and Užice Armies , with a combined strength of approximately 180 , 000 men . Serbia ' s last military campaign , the 1912 – 13 Balkan Wars , had only just concluded and the country was still recovering . Over 36 , 000 Serbian soldiers had been killed and 55 , 000 seriously wounded . Few recruits had been gained from the newly acquired territories , and the Serbian army had been stretched by the need to garrison them against Albanian insurgents and the threat of Bulgarian attack . To compound matters , the Serbian army was dangerously short of artillery , and had only just begun to replenish its ammunition stocks . Its supply problems also extended to more basic items . Many Serbian recruits reported for duty barefoot , and many units lacked any uniform other than a standard issue greatcoat and a traditional Serbian cap known as a šajkača . Rifles were also in critically short supply . It was estimated that full mobilization would see some 50 , 000 Serbian soldiers with no equipment at all . The Austro - Hungarians , on the other hand , possessed an abundance of modern rifles and had twice as many machine gun s and field gun s as the Serbs . They also had better stocks of munitions , as well as much better transport and industrial infrastructure behind them . The Serbs had a slight advantage over the Austro - Hungarians : many of their soldiers were experienced veterans of the Balkan Wars and better trained than their Austro - Hungarian counterparts . Serb soldiers were also highly motivated , which compensated in part for their lack of weaponry . Austro - Hungarian forces assigned to the invasion were placed under the command of General Oskar Potiorek , who had been responsible for the security detail of Archduke Franz Ferdinand in Sarajevo . Prior to the battle , Potiorek had predicted an easy victory over the Serbians , calling them " pig farmers . " The Serbian army was commanded by Crown Prince Alexander , with the Chief of the General Staff , Field Marshal Radomir Putnik , who had commanded Serb forces in the Balkan Wars , as his deputy and " de facto " military leader . Generals Petar Bojović , Stepa Stepanović and Pavle Jurišić Šturm commanded the 1st , 2nd and 3rd Serbian Armies , respectively . Prelude . From 29 July to 11 August , the Austro - Hungarian army launched a series of artillery attacks in northern and northwestern Serbia and subsequently managed to exploit the bombardments by constructing a system of pontoon bridges across the Sava and Drina Rivers . The Serbians knew that it was impossible for their forces to line the entirety of the Austro - Serbian border , which extended . Putnik therefore ordered the Serbian army to fall back on a traditional line of defence as he grouped the bulk of his forces in Šumadija , from where they could rapidly move either north or west . Strong detachments were posted in the towns of Valjevo and Užice , and outposts were stationed at every important point on the frontier . At this stage , all the Serbian General Staff could do was wait until the Austro - Hungarian invasion plan materialized . Belgrade , Smederevo and Veliko Gradište continued to be subjected to more vigorous artillery bombardments , and a number of failed attempts to cross the Danube resulted in heavy Austro - Hungarian losses . The bulk of the Austro - Hungarian forces were stationed in Bosnia , and the Serbian General Staff were not misled by these feints on the Danube . Subsequently , the Austro - Hungarians attempted to cross the Drina at Ljubovija and the Sava at Šabac , and these attacks were seen as more significant . On 12 August , Austro - Hungarian troops entered Serbia through the town of Loznica . There , and in the village of Lešnica , the Austro - Hungarian 13th Army Corps made a crossing , while on the same day the Austro - Hungarian 4th Army Corps crossed the Sava to the north of Šabac , while other Austro - Hungarian troops crossed the Drina . The town of Šabac was quickly taken . By 14 August , over a front of about , the Austro - Hungarians had crossed the rivers and converged on Valjevo . The Austro - Hungarian 2nd and 5th Armies moved towards Belgrade , where they encountered the Serbian 1st , 2nd and 3rd Armies . On 15 August , Marshal Radomir Putnik ordered his forces to launch a counterattack . Battle . Around 23 : 00 on 15 August , elements of the Serbian 1st Combined Division encountered outposts set up by the invading Austro - Hungarian army on the slopes of Cer Mountain and fighting erupted . The Austro - Hungarian positions were lightly held , and their defenders were driven back away from the mountain . By midnight , fierce clashes between the Austro - Hungarians and the Serbs were underway and chaos ensued in the darkness . By the morning of 16 August , the Serbians had seized the Divača Range and dislodged the Austro - Hungarians from their positions in the village of Borino Selo . The Austro - Hungarians , who had suffered heavy casualties during the fighting , retreated in some disorder . As the day progressed , the Serbs drove the 21st Infantry Division off the slopes of Cer to prevent it from linking with the 2nd Army in Šabac . On 17 August , the Serbs attempted to retake Šabac , but their efforts failed . The 1st Combined Division attacked the villages of Trojan and Parlog before moving on towards the small town of Kosanin Grad . Elsewhere , the Austro - Hungarians succeeded in repulsing the Serbian 3rd Army , forcing it to manoeuvre one of its divisions to protect the approach to the town of Valjevo , which was threatened by the 42nd Mountain Division . In the early morning of 18 August , the Austro - Hungarians launched another attack , with the intention of pushing the 1st Šumadija Division off the Šabac bridgehead to allow the 5th Army to advance . However , the attack failed as the Serbs defeated the Austro - Hungarians at the Dobrava River , forcing their surviving soldiers to withdraw . Elsewhere , the Serbian 2nd Army ' s counter - offensive continued along the Cer and Iverak , with the 1st Combined Division attacking the village of Rašulijača and coming under severe pressure at Kosanin Grad . The first Serbian assault was fought off , but a wave of further attacks followed throughout the night . In the early morning of 19 August , the Serbs finally defeated the Austro - Hungarians and seized the small town . The 1st Morava Division drove the 9th Infantry Division from its position and fought off the division ' s subsequent counterattack , inflicting heavy losses . The 4th Corps renewed its attack against the Šumadija Division , forcing the Serbs to withdraw having only sustained light casualties . Because the 4th Corps did not break the Serbs , the Austro - Hungarian division was unable to alter the direction of its advance towards Cer Mountain , since doing so would have put the Šumadija Division in a position to attack the 4th Corps from the rear . As a result , the 4th Corps was unable to join other Austro - Hungarian forces fighting at Cer . The Serbs retook Rašulijača at noon , and the 1st Combined Division exploited this to advance towards Lešnica . Meanwhile , the 1st Morava Division attacked Iverak and managed to drive the Austro - Hungarians back . The village of Velika Glava fell to the Serbs before mid - day , and by the late afternoon the Rajin Grob ridge had been retaken . At around this time , the Austro - Hungarians began retreating with increasing rapidity , their will and cohesion apparently shattered . The 3rd Army had similar success , routing the 36th Infantry Division and forcing it to retreat in considerable disorder . The Serbs then moved to pursue the fleeing Austro - Hungarians all along the front . By 20 August , Austro - Hungarian forces were fleeing across the Drina River , still being pursued by the Serbs back into Bosnia , with the entire 5th Army being forced across the Austro - Hungarian side of the river . Many Austro - Hungarian soldiers drowned in the water as they fled in panic . Serbian military reports announced that " the enemy is withdrawing in the greatest disorder . " Putnik then notified King Peter I in a telegram , saying " the main enemy has been defeated in Jadar and on Mount Cer , and our troops are in hot pursuit . " Upon their triumph at Cer Mountain , the Serbs sought to recapture the heavily fortified town of Šabac . Violent clashes occurred on 21 and 22 August , during which Serb forces fought their way to the western approaches of the town . By 23 August , the Serbs had encircled the town and that evening they brought up their siege artillery . On 24 August , Serbian forces entered Šabac and discovered that the Austro - Hungarians had decamped the previous night . By 16 : 00 , the Serbs reached the banks of the Sava River , bringing the first Austro - Hungarian invasion of Serbia to an end . Casualties . Both sides suffered heavy casualties in the battles . Estimates of the number of Austro - Hungarian casualties vary . Jordan states that the Austro - Hungarians suffered a total of 37 , 000 casualties in the battle , of whom 7 , 000 were fatalities . In contrast , Misha Glenny states that almost 30 , 000 Austro - Hungarian soldiers were wounded and 6 , 000 – 10 , 000 were killed . Horne writes that the Austro - Hungarians had 8 , 000 soldiers killed and 30 , 000 wounded in the battle , compounded by the loss of forty - six cannon , thirty machine guns and 140 ammunition wagons . Historian David Stevenson reports that 4 , 500 Austro - Hungarian soldiers were taken prisoner in the battle . Estimates of the number of Serbian casualties also vary . Horne and Jordan both agree that approximately 3 , 000 Serbian soldiers were killed and 15 , 000 were wounded in the battle . Glenny counters that 3 , 000 – 5 , 000 Serb soldiers were killed in the battle . Nevertheless , the number of fatalities suffered by both sides heralded the massive cost in human lives of the First World War . French journalist Henry Barby reported : Atrocities were committed by both the Austro - Hungarians and Serbs , although , according to author Lawrence Sondhaus , the majority were committed by the Austro - Hungarians only because they had more opportunities to do so . The Austro - Hungarians charged Serb civilians with mutilating Austro - Hungarians soldiers , while undisciplined Austro - Hungarian troops summarily executed hundreds of Serb men and raped and murdered numerous women and children during the battle , which Songhaus ascribes to their hatred towards Serbs for starting the war . Many of those murdered by the Austro - Hungarians were the victims of fellow South Slavs ( Serbs , Croats and Bosnian Muslims ) serving in the Austro - Hungarian army . Serbian commanders noted that Austro - Hungarian forces had committed numerous reprisal killings in Serbian villages during the battle . General Pavle Jurišić Šturm was quoted saying : Aftermath . Although they succeeded in repelling the Austro - Hungarian attack , the Serbs used up much of their ammunition during the battle , needing 6 . 5 million cartridges and 35 , 000 shells to prevail . The commander of the Serbian 2nd Army , General Stepa Stepanović , was promoted to the rank of field marshal ( ) after his successful command in the battle . Austro - Hungarian commander Oskar Potiorek , on the other hand , was humiliated by the defeat and was determined to resume the assault against the Serbs . He was given permission in September 1914 to launch another invasion of Serbia provided that he " not risk anything that might lead to a further fiasco . " Defeat at Cer Mountain also significantly affected the soldiers of the Austro - Hungarian army in the Balkans . Austro - Hungarian forces fighting in Montenegro were forced to abandon the town of Pljevlja , which they had captured on 19 August , because of the Austro - Hungarian army ' s defeat at Cer Mountain and subsequent withdrawal from Montenegro and Serbia back into Austria - Hungary . The first aerial dogfight of the war occurred during the battle , when a Serbian aviator encountered an Austro - Hungarian plane while performing a reconnaissance mission over Austro - Hungarian positions . The Austro - Hungarian pilot then fired at Serbian aviator Tomić with his revolver . Tomić managed to escape , and , within several weeks , all Serbian and Austro - Hungarian planes were fitted with machine - guns . Success in the battle drew worldwide attention to Serbia and won the Serbs sympathy from both neutral and Allied countries as it marked the first Allied victory over the Central Powers in the First World War . As a result , foreigners flocked to the country in late 1914 , offering financial , political , humanitarian and military aid . Articles in defence of the Serbs became more frequent in the British press and , according to historian Andrej Mitrović , Serbia was held in such high esteem that certain cultural groups in Italy advocated entering the war on the Allied side , citing Serbia and Montenegro as examples of opposition to the Austro - Hungarians . The Serbian patriotic song March on the Drina was written by Serbian composer Stanislav Binički shortly after the battle to commemorate the victory . Binički dedicated the march to his favourite commander in the army , Colonel Stojanović , who was killed during the fighting . A Yugoslavian war film also titled " March on the Drina " was released in 1964 and is loosely based on the battle .