Křída is a medieval castle ruin located in Jabloneček near Ralsko, within the Liberec Region of the Czech Republic. The site features remnants of an earthwork fortification with a notable moat that once separated it from other defensive structures. Despite its historical significance, no definitive written records exist about the castle's origins or early history. Archaeological findings include foundations of a stone building measuring approximately 15 by 6 meters.

The earliest known mention of Křída dates back to 1356 in a predikát associated with Peška Kabát z Křídy. Another reference from 1396 suggests that Mutyně z Křídy resided there, supported by archaeological evidence such as dated ceramic fragments. This period was marked by feudal development within Bohemia, part of the Holy Roman Empire, where many castles were constructed to establish noble power and protect territories.

Architecturally, Křída had a triangular layout, characterized by its prominent moat, which remains one of its most notable features today. Archaeological investigations from the late 1960s revealed stone building foundations, indicating significant construction efforts during its existence. The castle's design reflects typical medieval fortification strategies aimed at defense and control.

Ownership of Křída is documented through historical figures such as Peška Kabát z Křídy in 1356 and Mutyně z Křídy in 1396. These individuals were likely part of the local nobility, reflecting the feudal system's influence on property ownership during that era. The lack of extensive records leaves much about its administration and fortunes to speculation.

The site is located within a former military area near Ralsko, featuring natural elements like the Zábrdka stream. While no marked paths lead directly to the ruins, they can be accessed via a road from Cetenov, with an unmarked trail leading to the remnants of Sauermühle mill nearby.

Today, Křída stands as a testament to medieval architecture and history, offering visitors a glimpse into the past through its preserved earthworks and foundations. Although no definitive written records exist about its origins, archaeological findings provide valuable insights into its construction and use. The site's accessibility via local roads makes it an intriguing destination for those interested in exploring historical ruins and understanding the region's medieval heritage.

Visiting Křída offers a unique opportunity to connect with the past, standing amidst remnants that speak of centuries-old stories and architectural ingenuity. It invites history enthusiasts and curious travelers alike to explore its silent yet significant presence in the Czech landscape.