The concept of the "strongest" sword in the world is subjective and can vary depending on different criteria and perspectives. Strength can be evaluated based on various factors such as hardness, flexibility, durability, cutting power, historical significance, or cultural impact. Here are a few swords that are often considered remarkable in terms of their strength:

1. Damascus Steel Swords: Damascus steel swords, known for their exceptional sharpness and resilience, are highly regarded for their strength. The historical technique of forging Damascus steel involved layering and folding different types of steel, resulting in a blade with superior strength, flexibility, and edge retention.
2. Ulfberht Swords: Ulfberht swords were medieval Viking swords that stood out for their high-quality craftsmanship and advanced metallurgical techniques. These swords were made of high-carbon crucible steel, which gave them superior strength and durability compared to many contemporary swords.
3. Katana: The traditional Japanese katana is revered for its strength and cutting ability. Crafted through a meticulous process of folding and differential hardening, the katana exhibits a combination of hardness, flexibility, and sharpness. The quality of the steel and the skill of the swordsmith are crucial factors in determining the strength of a katana.
4. Oakeshott Type XVII Swords: Oakeshott Type XVII swords, also known as "hand-and-a-half" swords, were popular during the medieval period in Europe. These swords were known for their strength and versatility, with a design that balanced cutting and thrusting capabilities.

It's important to note that the strength of a sword depends not only on the materials used but also on the quality of craftsmanship and the specific design and purpose of the sword. Furthermore, historical and cultural contexts can influence the perception of strength and the significance of different swords. The strength of a sword is often evaluated based on a combination of factors and should consider the intended use and cultural background associated with the weapon.