They consolidated the position of Brandenburg within the Holy Roman Empire, which was reflected in the fact that in 1256, Otto III was a candidate to be elected King of the Germans.

Since John and his two-year-younger brother Otto III were minors when their father died in 1220, Emperor Frederick II transferred the regency to Archbishop Albert I of Magdeburg.

In 1221, their mother, Countess Matilda, purchased the regency from the Archbishop of Magdeburg for 1900 silver Marks and then ruled jointly with Henry I.

[1] The Archbishop of Magdeburg then travelled to Italy to visit Emperor Frederick II, and Duke Albert I of Saxony attempted to grab power in Brandenburg, causing a rift with his brother Henry I.

[2][3] After the death of Count Henry of Brunswick-Lüneburg in 1227, the brothers supported his nephew, their brother-in-law Otto the Child, who was only able to prevail against Hohenstaufen's claims and its vassals by force of arms.

After the dispute over the kingship between Conrad IV and Henry Raspe the brothers recognized William II of Holland as King in 1251.

Although Alfonso was not elected, the fact that they could vote illustrates the growing importance of Brandenburg, founded only a century earlier, in 1157, by Albert the Bear.

By the 1230s, the Margraves of Brandenburg had gained the heritable post of Imperial Chamberlain and the indisputable right to vote in the election of the King of the Germans.

On 20 June 1236, the Margraviate acquired the Lordships of Stargard, Beseritz, and Wustrow by the Treaty of Kremmen from Duke Wartislaw III of Pomerania.

At stake was a Slavic castle at Köpenick, a former headquarters of the Sprewanen tribe, located at the confluence of the Spree and Dahme rivers.

In 1257, John I founded the town of Landsberg (now called Gorzów Wielkopolski) as an alternative river crossing across the Warta, competing with the crossing in the Polish town of Santok, detracting from the considerable revenues Santok made from foreign trade (customs duties, fees from the market operation and storage fees), similar to the way Berlin had been founded to compete with Köpenick.

In 1261, the Margraves purchased Myślibórz (German: Soldin) from the Knights Templar and began developing the town into their power center in the Neumark.

Their cooperation with the Polish count provided border security against Pomerania and prepared the area's economy for integration into the Neumark.

The small town of Cedynia (Zehden; today in the Polish Voivodeship of West Pomerania) was enfeoffed to the noble von Jagow family.

The historian Stefan Warnatsch has summarized this development and the attempts of the Ascanians to gain access to the Baltic Sea from the middle Oder and the Uckermark as follows: The great success of the territorial expansion in the 13th century was mainly due to the great-grandsons of Albert the Bear.

For a long time, the border between the territories of the Slavic tribes Hevelli and Sprewanen crossed straight through the area of today's Berlin.

Towards the end of the 12th century, the Ascanians moved the fortress about a kilometer to the North, to the location of today's Spandau Citadel, probably because of a rising ground water table.

[11] The ford across the largely swampy Berlin Glacial Valley gained importance during the Slavic-German transition period, when John I and Otto III settled the sparsely populated plateaus of Teltow and Barnim with local Slavs and German immigrants.

The Margraves protected the route to Halle across the northwestern Teltow plateau by a chain of Templar villages: Marienfelde, Mariendorf, Rixdorf and Tempelhof.

After the Ascanians defeated the Wettins in the Teltow War of 1245, the importance of Köpenick decreased, took an increasingly central position in the developing trading network.

[12] According to Winfried Schich, we can assume the "Berlin and Cölln owe their development as urban settlements to the structural changes in this area due to the expansion during the High Middle Ages, which led both to a denser population and a reorganization of long-distance trade routes.

[...] The diluvial plateaus of Teltow and Barnim with their heavy and relatively fertile soils, were systematically settled and put under the plow during the reign of Margraves John I and Otto III.

The preparations for the reorganization may have begun in 1250, when the Uckermark was acquired, but no later than 1255, when John I married Jutta (Brigitte), the daughter of Duke Albert I of Saxony-Wittenberg.

[17] The politics of marriage and 1258 consummated division of the state government led to the joint foundation of the monastery of Mariensee on a former island in the Parsteiner See lake on the northeastern edge of today's Barnim.

Even before Marinesee was completed in 1273, a decision was made to move to a new location approximately five miles to the southwest with the new name Chorin Abbey.

[18] It appears that in 1266, John I arranged for the monastery to move and that he donated rich gifts to the new Chorin Abbey, including the village of Parstein.

[22] Their successors as Margraves of Brandenburg, Otto IV "with the Arrow", Waldemar "the Great" and Henry II "the Child" all stem from the Johannine line.

The Siegesallee was a grand boulevard commissioned by Emperor Wilhelm II in 1895 with statues illustrating the history of Brandenburg and Prussia.

Each statue was flanked by two smaller busts representing people who had played an important rôle in the life of the historic ruler.

Two adolescents would not have been able to adequately express the founding of a future world city, from the perspective of the late 19th century interpretation of history.