How to use xmllint to validate an XML document with an XSD?

I'm trying to use xmllint to check my work while developing a basic XSD i.e. XML Schema Definition. However it's giving me an error:

Validation failed: no DTD found.

What am I doing wrong?

My xmllint command:

xmllint --noout --valid --schema simple.xsd lucas-basic.xml
lucas-basic.xml:5: validity error : Validation failed: no DTD found !
        >
        ^
lucas-basic.xml validates

Test XSD file:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="vehicles">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element name="nickname" type="xsd:string" maxOccurs="unbounded"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>
</xsd:schema>

Test XML file:

<?xml version="1.0"?>
<vehicles xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:noNamespaceSchemaLocation="http://lucas.ucs.ed.ac.uk/xml-schema/xmlns/simple.xsd">
  <nickname>Bog Hopper</nickname>
  <nickname>Wee Beastie</nickname>
  <nickname>Count Zero</nickname>
</vehicles>

The URL at xsi:noNamespaceSchemaLocation does return the above XSD. Also, I downloaded the XSD file and put it into the current directory as an extra measure, but this didn't seem to have changed anything.

--valid is for DTDs, not XSDs.

This will work for you instead:

xmllint --noout --schema http://lucas.ucs.ed.ac.uk/xml-schema/xmlns/simple.xsd lucas-basic.xml