The word qasaba (or kasbah, gasaba, quasabeh) comes from the Arabic القصبة, meaning "central part of a town or citadel". In the Zahrani dialect, and for purposes of this article, "qasaba" refers to a single stone tower or tower house found frequently in the Asir and al-Bahah provinces of Saudi Arabia and in Yemen.
The purposes of the qasaba (plural forms are: "qasabi" or "qasabe" in Arabic; "kasabalar" in Turkish; "qasabas" in English) are varied, and they often functioned as an isolated watch tower or blockhouse. However, in Morocco and in Iberia, the Arabic word form of " kasbah" frequently refers to multiple buildings in a keep, a citadel or several structures behind a defensive wall. The Spanish word " alcazaba" is a cognate from the Arabic word. In Portuguese, it derived into the word alcáçova. In Turkish and Urdu the word kasaba refers to a settlement larger than a village but smaller than a city; in short, a town. The Cyrillic spelling is каса̀ба.
The Encyclopædia Britannica defines it as: "Ancient qasaba (“towers”) found in the province were used as lookouts or granaries."
Another book describes these towers as follows: "Apparently unique to Asir architecture are the qasaba towers. Controversy surrounds their function - some argue that they were built as lookouts, and others that they were keeps, or even granaries. Perhaps it is a combination, although the right position of a watchtower, on a hill top, is the wrong place for a keep or granary."
Archeologists have found images of similar towers in the ruins of Qaryat al-Fāw, in the Rub' al-Khali or the Empty Quarter of Saudi Arabia, that date from between the third century BCE to the 4th century or our era. "Homes rose two stories, supported by stone walls nearly two meters (6') thick and boasting such amenities as water-supply systems and second-floor latrines. One eye-catching mural faintly depicts a multi-story tower house with figures in the windows: Its design resembles similar dwellings today in Yemen and southern Saudi Arabia."
"Most of the qasabas have a circular plan, although some are square. Sometimes they have a band of quartz stones just below the windows or framing the windows- one well preserved examples is at the top of Wadi Ain. The remains of a martello tower-like stone structure are just off the dirt track north of Al-Masnah. It appears to be an interesting antecedent of the Asir farmhouse and perhaps closely related to the qasaba. It is in ruins now, but was once a dwelling and is strongly defensive."
One account says about a traditional village in Al-Baha, Saudi Arabia: "Even the road that leads to the village is impressive, and several historical stone and slate towers dot the way. Al-Bahah Province is known as the region of 1001 towers, once built to protect villages, roads and plantations from rivalling tribes. Today, these towers are abandoned, and many of them are partially or completely in ruins."