The Romanian government asserted that the moment was right for it to fulfill the country's national ambitions by aligning itself with the Entente, and declared war on the Austro-Hungarian Empire on 27 August 1916.

In a short time the Romanian forces occupied Orșova, Petroșani, and Brașov, and reached Sibiu on their way to the river Mureș, the main objective of the offensive.

The enormous width of the river, however, proved insufficient to defend against the armies of the Russian Empire, which crossed it several times in its lower stretch during the numerous Russo-Ottoman Wars.

To counter this constant threat the Ottoman military created the fortified quadrilateral Ruse–Silistra–Varna–Shumen, hoping to prevent any invaders from crossing the Balkan Mountains and threatening Istanbul.

With the liberation of Bulgaria after the Russo-Turkish War (1877–1878), Tutrakan became an integral part of the country, but Bulgarian national ambitions were directed in general towards Macedonia and Thrace, and the defense of the Danube was largely neglected.

The line stretched for almost 30 kilometers and had as its heart fifteen "centers of resistance", forts numbered from one to 15 and bearing the names of local settlements - "Turtucaia", "Staro Selo", "Daidâr", "Sarsânlar" etc.

For command purposes the entire area of the fortress was divided into three sectors: I (west), II (south) and III (east), also named after local villages - Staro Selo, Daidâr, and Antimova.

[8] The garrison of Turtucaia was connected to Olteniţa, which lay across the Danube, by a submerged telephone cable, and to Third Army headquarters in Bucharest by a wireless telegraph station; however, it remained relatively isolated from the nearest Romanian units in Dobruja.

[7] To protect their Danube frontier the Bulgarians had activated their Third Army as early as September 1915, giving its commander, Lieutenant General Stefan Toshev, almost a year to train and equip his troops.

[12][13] This ensured the initial numerical superiority of the attackers both in men and firepower, but most of the Bulgarian units, with the notable exception of the 1st Brigade of the 1st Sofia Infantry Division, did not have direct combat experience, as they did not take part in the Serbian Campaign.

Nonetheless general Kiselov and his chief of staff Lieutenant Colonel Stefan Noykov were rated excellent officers by the Germans and represented the top divisional leadership in the Third Army.

On 28 August field marshal Mackensen issued his first directive to the Bulgarian Third Army, ordering it to prepare for a decisive advance aimed at seizing the vital crossing points on the Danube in Southern Dobruja.

On the same day Toshev presented a detailed plan for the assault, according to which the army would advance on 2 September with its left wing against the bridgehead while the 3/1 Infantry Brigade moved in the direction of Silistra to cover its flank.

On the next day von Mackensen approved the plan with minor adjustments, such as requiring that the 2/1 Infantry Brigade be kept in reserve for the defense of the right flank of the forces attacking Turtucaia.

[14] The Romanian plan, or the so-called Hypothesis Z, required most of the country's forces to invade Transylvania, while its almost 150,000-strong Third Army assumed a defensive stance along the Danube and Dobruja frontiers for ten days.

[16] Meanwhile, in Sector III (East) the Bulgarian 1/1 Infantry Brigade met no resistance at all, as the Romanian commander had pulled his troops behind the main defensive line before coming under attack.

The defenders here were relatively well entrenched and protected by rows of barbed wire, while the attackers had to advance through an open field with their flanks exposed to fire from the Romanian monitors and some of the trenches.

After a rainy night the 4th Preslav Division used 3 September to approach the barbed wire of the main defensive line in Sector II, driving away Romanian patrols, taking Daidâr (now Shumentsi), and repositioning its heavy artillery.

It stated that the commander of the 4th division was to assume control over all forces operating against the fortress and determine the exact hour of the infantry attack, once the preliminary artillery barrage had inflicted sufficient damage.

In addition, communication with von Hammerstein's group was weak, and the two German minenwerfer companies that were crucial for the advance in that sector needed more time to position themselves.

Active fighting continued only in Sector I, where von Kaufman's detachment had to finish the attack on height 131, which it had started the previous day, and secure the staging ground for the assault on fort 2.

This time he was not ignored: the 10th and 15th divisions, representing the army's strategic reserve, were ordered to move south towards Olteniţa - the first to guard the river shore and the latter to prepare to cross the Danube and assist the garrison in Turtucaia.

[13] These new, fresh troops allowed the Romanians to gain numerical superiority over the Bulgarians, but once again they were delayed on their way and would arrive gradually on the battlefield, reducing their impact on the overall course of the battle.

In Sector III the artillery bombardment began at 6:55, and by 8:15 had achieved considerable success in damaging the Romanian fortifications, forcing some of the defenders to flee to the rear and the Danube.

Meeting little resistance, as the arriving Romanian reinforcements were often caught up by retreating units and compelled to join them, the Bulgarians accomplished this task and by 21:30 reached the shore of the Danube, completing the isolation of the fortress.

Despite the artillery fire they faced, the Bulgarians and Germans advanced with relative ease as the Romanians, despite their large number, began retreating and even fleeing in panic to Turtucaia.

On 6 September these forces were met and defeated by the Bulgarian 3/1 Infantry Brigade, which had been ordered to protect the flank of the army, at the village of Sarsânlar (now Zafirovo), some 18 kilometers to the east of Turtucaia.

At 15:30 colonel Mărășescu, who was now in charge of the garrison, and his senior officers wrote a note to general Kiselov in German and dispatched it to three of the sectors, offering the unconditional surrender of the fortress together with all its men and material.

The speed with which the victory was achieved was so unexpected by the Central Powers that even Field Marshal Mackensen, who was usually present on the site of important battles, hadn't planned to arrive on the battlefield until several days after the actual capitulation of the fortress.

Kaiser Wilhelm, who had been particularly depressed by Romania's entry into the war, celebrated with a champagne party for the Bulgarian representative at the headquarters of the German High Command.