a notary of King Béla III mention Hungarian victories against Croatia in the same period, however, both sides had gains. Croatia maintained its northern borders and expanded into part of the collapsed Pannonian Duchy, including its former capital Sisak. The plains north of Sisak were difficult to defend against Hungarian cavalry, but Sisak had been well-fortified since the reign of Duke Ljudevit. The sparsely-populated area between the Sava and Drava rivers was on the outskirts of Hungary and the Duchy of Croatia (centered on the coast), so neither country could strengthen its rule there after the Duchy of Pannonia dissolved. East of Croatia, the First Bulgarian Empire's power increased significantly. After a war between the Bulgarian knyaz Boris I and Croatian Duke Trpimir I, Croatian-Bulgarian relations were fairly good. Papal legates regularly crossed Croatian territory (where they received protection) to Bulgaria. The situation changed in the 10th century during the reign of Simeon I, who decided to subordinate the Byzantine Empire to himself. Tomislav's realm covered most of southern and central Croatia and the Dalmatian coast, excluding the Theme of Dalmatia, parts of present-day western Herzegovina and northern and western Bosnia. During the early 10th century, Croatia was divided into 11 counties: Livno, Cetina, Imotski, Pliva, Pset, Primorje, Bribir, Nona, Knin, Sidraga, and Nin. Three counties (Lika, Krbava, and Gacka) were ruled by a ban. After its expansion, Tomislav's state presumably contained more than eleven counties. Byzantine emperor and chronicler Constantine VII writes in De Administrando Imperio that at its peak, Croatia could have raised a military force composed of 100,000 infantry, 60,000 horsemen, and a naval fleet of 80 large ships and 100 smaller vessels. However, these figures are viewed as a considerable exaggeration of the size of the Croatian army. According to palaeographic analysis of the manuscript of De Administrando Imperio, the population of medieval Croatia was estimated at 440,000 to 880,000; its military force probably consisted of 20,000–100,000 infantrymen and 3,000–24,000 horsemen organized into 60 allagia. Coronation and Croatian kingdom Tomislav had become King of Croatia by 925, and was the first Croatian ruler whom the papal chancellery called "king". It is generally said that Tomislav was crowned in 924 or 925, but it is not known exactly when, where, or by whom. Letters in which Tomislav was called king were preserved in a version of Thomas the Archdeacon's 13th-century History of Salona. A note preceding the