the River Halmyros—a small stream between Herakleia (modern Marmara Ereğlisi) and Selymbria (modern Silivri), modern Kalivri Dere—near the fort of Kalavrye (, modern Yolçatı). Curiously, and against established practice, he did not fortify his camp, perhaps so as not to fatigue or dishearten his men with an implicit admission of weakness. He then sent his Turkish allies to scout out Bryennios's disposition, strength, and intentions. Alexios's spies easily accomplished their tasks, but on the eve of the battle some were captured and Bryennios too was informed of Alexios's strength. Battle Initial dispositions and plans Bryennios arranged his army in the typical three divisions, each in two lines, as prescribed by the Byzantine military manuals. The right wing, under his brother John, was 5,000 strong and comprised his Frankish mercenaries, Thessalian cavalry, the Hetaireia, and the Maniakatoi regiment (descendants of the veterans of George Maniakes's campaign in Sicily and Italy). His left wing, 3,000 men from Thrace and Macedonia, was placed under Katakalon Tarchaneiotes, and the centre, under Bryennios himself, comprised 3,000–4,000 men from Thessaly, Thrace, and Macedonia. Again, according to standard doctrine, on his far left, about half a kilometer ("two stadia") from the main force, he had stationed an outflanking detachment (hyperkerastai) of Pechenegs. Alexios deployed his smaller army in waiting near Bryennios's camp, and divided it into two commands. The left, which confronted Bryennios's strongest division, was commanded by himself and contained the Frankish knights to the right and the Immortals to the Franks' left. The right command was under Constantine Katakalon, and comprised the Chomatenoi and the Turks. The latter, according to the Alexiad, were given the role of flank guard (plagiophylakes) and tasked with observing and countering the Pechenegs. Conversely, on the extreme left Alexios formed his own flanking detachment (apparently drawn from among the Immortals), concealed from enemy view inside a hollow. Given his inferiority, Alexios was forced to remain on the defensive. His only chance at success was that his out-flankers, concealed by the broken terrain, would surprise and create enough confusion among Bryennios's men for him and his strong left wing to break through their lines. Alexios's army collapses As the rebel forces advanced towards his enemy's line, Alexios's flankers sprung their ambush. Their attack did indeed cause some initial confusion, but Bryennios (or, according to the Alexiad, his brother John, who commanded the right wing) rallied his men and led forth the