Karasawayama Castle is one of the seven most famous castles of the Kanto area and is considered by many to have been the best mountaintop castle. It earned this recognition from withstanding 10 attacks by the Uesugi during the Sengoku Period.

In Hideyoshi's campaign against the Hojo, Sano sided with Hideyoshi. At that time, the Sano were in good relations with the Hojo so he removed all the Hojo from the castle. At the Battle of Sekigahara the Sano sided with Tokugawa.

It is said that in 1602 when there was a great fire at Edo Castle, the fire could be seen from the top of Karasawayama Castle. When he saw this, Sano sent his messengers to Edo Castle to relay his condolences. However, from this event it came to the attention of the Tokugawa that Karasawayama Castle looked down upon Edo Castle so the Sano were forced to abandon it and rebuild a new castle (Sano Castle) on a lower elevation.

It is also said that the Tokugawa claimed there was a law against mountaintop castles in the vicinity of Edo. Unfortunately, there is no proof that either of these stories is true. Regardless, the Sano moved their castle from Karasawayama to a nearby location in 1602.