Already in the late 1950s one of the authors of this book, archaeologist Andris Caune, planned to write a lexicon of Latvian castles. However, his permanent research work in Riga, the writing of articles and monographs on the results of that research, as well as large-scale fieldwork on the Bauska castle (in the 1970s-1980s) took up all his time. Only in the 1990s, when his daughter, art historian Ieva Ose, had become his match as a research companion, the opportunity appeared to realize the plan designed several decades before. To start with, Ieva Ose made a thorough study of the archival materials and archaeological literature available in Riga and Stockholm, as well as in Estonia. Fieldwork and photographing started in 1997. This approach gave an opportunity to proceed from the individual to the general, and already in 1999 Ieva Ose could publish the first volume of the series concerning Latvian castles--materials of the symposium .Latvijas viduslaiku pilis, I. (Medieval Castles of Latvia, I), focused mainly on the medieval castles of the Archdiocese of Riga. A review of the collected archival information was published in Ieva Ose.s next book, the historiographic monograph "Latvijas viduslaiku pilu petnieciba 18.-20. gadsimta" (Studies of the Medieval Castles of Latvia in the 18th-20th Centuries), which was published in 2001. The next subject to be handled was the Order's castles on the territory of present-day Latvia, leading to the publication of the third volume of the series, "Petijumi par ordenpilim Latvija" (Studies of the Order's Castles of Latvia), written by 15 researchers and compiled/edited by Ieva Ose. And now, in 2004, we hold the general lexicon of Latvian castles "Latvijas 12. gadsimta beigu-17. gadsimta vacu pilu leksikons" (Latvijas viduslaiku pilis, IV). Actually this miscellany did not appear on a vacant space either. Since the publication of the German translation by Johann Gottfried Arndt of the chronicle of Henry of Livonia in 1753, with an appendix providing a table of the castles, towns and monasteries of Old Livonia, researchers have, ever and again, returned to the subject: the castles, established by Germans, remained administrative and economic footholds of foreign power for centuries, still arousing interest in considerably later times. This is clearly proven by the review by Andreas von Lowis of Menar "Uber die Entstehung, den Zweck und den endlichen Untergang der Ritterschlosser im Alten Livland" // mitt.-Riga; Leipzig, published in 1840, as well as Alexander von Richter's study of a somewhat later date. Karl Lowis of Menar was indisputably a great figure in this field, regarding not only Latvia but also Estonia. He started his research, as well as writing respective articles, in 1888. During the nearly forty years to follow he managed to publish more than thirty papers enfolding the region from Narva to Klaipeda (Memel). Besides doing separate studies of sacral and profane architecture (also in Tallinn and Narva), his main attention was turned to castle architecture. The crown jewel of his study is the "Burgenlexikon fur Alt-Livland", published in Riga in 1922. Its 127 pages of text and 63 drawings comprise most of the information known to that day about the castles of Old Livonia. Owing to the scantiness of fieldwork the publication naturally enough could not achieve perfection, and certainly not the academic weight either. Since archaeological research both in Latvia and Estonia, particularly concerning medieval castles, in the period between the two World Wars was relatively inactive, a new quality was offered only 20 years later by Armin Tuulse, who defended and published his doctoral dissertation "Die Burgen in Estland und Lettland" (Dorpat, 1942). Unlike many earlier (and also later) researchers, Armin Tuulse was able (thanks to the scholarship from the University of Tartu) to study the castles of Germany, Holland, Belgium, France and Italy in 1937-38, and also to do research in the archives of Riga, Stockholm and Koningsberg. …