The Battle of Cer also known as Battle of Jadar (the main operations were held near the estuary of the Jadar)river. One of the first battles of World War I, it also marked the first Allied victory in the war. The battle was fought between the Austro-Hungarian Army and Serbian forces. Results improved Serbian standing in the Alliance. Western faith in the competence of the Serbian Army was vastly improved. Austro-Hungarian troops fought under the command of General Oskar Potiorek and Liberius von Frank who was in direct command of Austro-Hungarian forces at Cer and Serbian troops under the command of General Stepa Stepanović.

Battle Summary
When the First World War started the Austro-Hungarian Army under the command of General Oskar Potiorek pushed into northwestern Serbia across the Sava and the Drina. Šabac fell. Following the expansion of bridgeheads, most elements of 2nd and 5th army succesfuly crossed into Serbia by 12th August. Potiorek's own 6th army was still concentrating further south and was in no position to begin large operation at this time, so the brunt of the fighting in following days was on the 5th Army. According to Potjorek's plan, it was to attack in the general direction of Valjevo immediately after the crossing and take the city in five days.

Serbian Response
Another thing of great importance during Cer battle was Putnik's unwillingness to conduct aggressive offensive maneuvers (this was also the case in the First Balkan War) due to his fear of unnecessary risk which could lead to higher casualties in already undermanned Serbian army. An evident example was his overruling of General Stepanović's proposal on the eve of the third day of the battle. Stepanović sensed that Austro-Hungarian forces on Cer an Everk were beginning to crumble, so he suggested a bold maneuver in which his Kombinovana and Moravska divisions would conduct a forced frontal pursuit of opposing troops on Cer and Everk ridges, whilst the Cavalry and Timočka (this division was hardly used during the entire course of the battle, to significant dissadvantage regarding the outcome) divisions would conduct a parallel pursuit on the northern slope of Cer towards Lešnica, with orders to attack both the enemy's flanks and to reach the pontoon bridges on Drina river and therefore cut Fifth Army's main line of retreat. If this maneuver was conducted, possibillity of a catastrophe for Austro-Hungarian arms was significant. Yet, Putnik ordered Stepa to pursuit enemy force frontally and not to conduct any sort of flanking attack, which would, in itself, cause far larger casualties upon retreating enemy. Third Army's loss of contact with enemy on the third day of the battle also helped Austro-Hungarian Fifth Army to withdraw in a more orderly fashion. Considering this information, it is obvious that the invading force could have suffered a far costlier defeat and shows Putnik as a superb organiser (his mobilisation plans for both Balkans wars and World War I were excellent, considering the low quality of roads in Serbia and lack of a significant railroad network), yet overcautious in the conduct of battles.
During August 1914 a battle was waged in the area of Mt. Cer, in which around 200,000 Austro-Hungarians fought against 180,000 Serbs. The main battle at Cer lasted from August 16 to 19. The Serbian Army won the victory, pushed the Austro-Hungarian Army back across the Drina, and completely thwarted their war plan.

Outcome
Historical artifacts can be found in a museum located in the town of Šabac.